Treatment of leukemia with a imidazo carbamate

ABSTRACT

Use of Methyl N-[6-(3,4,5-trimethoxybenzyloxy)imidazo [1,2-6]pyridazin-2-yl]carbamate or pharmaceutically acceptable salt to treat lymphocytic leukemia is disclosed.

This is a division of application Ser. No. 08/123,529 filed on Sep. 17,1993, now U.S. Pat. No. 5,380,759, which is a division of Ser. No.07/817,539 filed Jan. 7, 1992, now abandoned, which is a continuation ofSer. No. 07/231,894 filed Aug. 12, 1988, now U.S. Pat. No. 5,091,531.

The present invention relates to heterocyclic compounds which have beenfound to have cytotoxic activity. More specifically, the inventionconcerns imidazopyridazine derivatives, methods for their preparation,pharmaceutical formulations containing them and their use as cytotoxicagents, in particular as antitumour agents.

Research in the area of cancer chemotherapy has produced a variety ofantitumour agents, which have differing degrees of efficacy. Standardclinically used agents include adriamycin, actinomycin D, methotrexate,5-fluorouracil, cis-platinum, vincristine and vinblastine. However,these presently available anti-tumour agents are known to have variousdisadvantages, such as toxicity to healthy cells and resistance tocertain tumour types.

In addition to having anti-tumour activity, vincristine is known to bean inhibitor of microtubule function. Other compounds which exhibitmicrotubule inhibitory activity and which have been reported to bepotential antitumour agents are nocodazole, tubulazole and NSC-181928;##STR1##

However, none of these compounds has yet been proven clinically.

There is thus a continuing need for new and improved anti-tumour agents.

We have now found a novel class of imidazopyridazine derivatives whichexhibit potent anti-tumour activity.

In a first aspect, the present invention provides a compound of generalformula (I) ##STR2## wherein

R¹ represents an optionally substituted carbocyclic or heterocyclic arylgroup, or an optionally substituted alkyl, alkenyl, cycloalkyl orcycloalkenyl group;

R² represents an optionally substituted alkyl, alkenyl, alkynyl,cycloalkyl or cycloalkenyl group or an optionally substitutedcarbocyclic or heterocyclic aryl or aralkyl group;

R³ represents a hydrogen atom or an alkyl group;

and either

X represents an oxygen or sulphur atom, a group --CH₂ -- or a group NR⁴where R⁴ represents a hydrogen atom or a C₁₋₄ alkyl group; and

Y represents a group --CH₂ -- or --CH₂ CH₂ -- or

X--Y together represent the group

    --CH═CH--;

and salts and physiologically functional derivatives thereof.

Referring to the groups R¹ and R² in the general formula (I) acarbocyclic aryl group may contain 6 or 10 ring members, e.g. phenyl andnaphthyl, and contains at least one aromatic ring. A heterocyclic arylgroup may contain from 5-10 atoms in the ring, at least one of which isa heteroatom. The heterocyclic ring typically contains from 1-4heteroatoms selected from nitrogen, oxygen and sulphur. Examples ofsuitable heterocyclic rings include thienyl, furyl, pyridyl, indole andquinoline rings.

Substituents which may be present on the carbocyclic or heterocyclicaryl group include C₁₋₆ alkyl, C₁₋₄ alkoxy (which may itself beoptionally substituted by a C₁₋₂ alkoxy or C₁₋₂ alkoxy-C₁₋₂ alkoxygroup), halogen (e.g. fluorine, chlorine or bromine), amino (optionallysubstituted by one or two C₁₋₄ alkyl groups), C₁₋₄ haloalkyl (e.g.trifluoromethyl), C₁₋₄ alkylthio, carboxy, C₁₋₄ alkoxycarbonyl, --SO₃ H,cyano and phenyl. The carbocyclic or heterocyclic anyl group maysuitably carry from 1 to 4 substituents.

Unless otherwise indicated, alkyl groups R¹ and R² present in generalformula (I) may be straight or branched chain alkyl groups, and maycontain 1-10 carbon atoms, e.g. 3-10 carbon atoms. An alkenyl or alkynylgroup may contain 2-10 carbon atoms e.g. 3-10 carbon atoms. A cycloalkylor cycloalkenyl group may contain from 3-10 carbon atoms. Substituentswhich may be present on an alkyl, alkenyl, alkynyl, cycloalkyl orcycloalkenyl group include halogen atoms, C₁₋₄ alkoxy groups, hydroxy,amino (optionally substituted by one or two C₁₋₄ alkyl groups) C₁₋₄haloalkyl (e.g. trifluoromethyl), C₁₋₄ alkylthio, carboxy, C₁₋₄alkoxycarbonyl, --SO₃ H and cyano.

When R² represents an aralkyl group this may contain from 1 to 4 atomsin the alkyl portion and the aryl portion may be a carbocylic orheterocyclic aryl group as defined above for R¹ and R².

When R¹ represents an alkyl group this preferably contains more than twocarbon atoms, e.g. C₃₋₆ alkyl.

When R² represents an alkyl group this preferably contains from 1 to 6carbon atoms, e.g. 1 to 4 carbon atoms.

When R³ or R⁴ represents an alkyl group this may be straight or branchedchain and may contain 1-4 carbon atoms.

Certain compounds of formula (I) may form salts. Thus, compounds (I)which contain a basic amino group may form salts with acids, andcompounds which contain an acidic group may form salts with bases.

Suitable acid addition salts include those formed from hydrochloric,hydrobromic, nitric, perchloric, sulphuric, citric, tartaric,phosphoric, lactic, benzoic, glutamic, oxalic, aspartic, pyruvic,acetic, succinic, fumaric, maleic, oxaloacetic, isethionic, stearic,phthalic, methanesulphonic, p-toluene sulphonic, benzenesulphonic,lactobionic and glucuronic acids. Suitable base salts include inorganicbase salts such as alkali metal (e.g. sodium and potassium) salts andalkaline earth metal (e.g. calcium) salts; organic base salts e.g.phenylethylbenzylamine, dibenzylethylenediamine, ethanolamine anddiethanolamine salts; and amino acid salts e.g. lysine and arginine.Most preferably, the salts will be pharmaceutically acceptable.

In the compounds of general formula (I) R¹ preferably represents anoptionally substituted phenyl or naphthyl group, an optionallysubstituted 5-or 6- membered heterocyclic aryl group, containing from 1to 4, e.g. 1 or 2, heteroatoms selected from nitrogen, oxygen andsulphur. Preferred substituents which may be present in the group R¹include C₁₋₄ alkoxy, C₁₋₄ alkyl, and mono-or-di-(C₁₋₄)alkylamino groupsand halogen atoms. R¹ further preferably represents an unsubstitutedalkyl group, e.g. a C₃₋₆ alkyl group.

R² preferably represents a phenyl group or an optionally substitutedC₁₋₄ alkyl group. Preferred substituents which may be present in thegroup R² include C₁₋₄ haloalkyl (e.g. trifluoromethyl), C₁₋₄ alkoxy,hydroxy, halogen, mono-or-di-(C₁₋₄)alkylamino and nitrogen-attached5-or-6 membered heterocyclic groups (e.g. morpholino, piperidino,pyrrolidino). Advantageously R² is a C₁₋₄ alkyl group.

R³ is preferably hydrogen or methyl.

Y preferably represents --CH₂ --. The group --Y--X-- preferablyrepresents --CH₂ O--, --CH₂ S--, --CH₂ CH₂ -- or --CH═CH--

A particularly preferred group of compounds of formula (I) are those inwhich

R¹ represents a phenyl or naphthyl group which may be substituted by 1to 4 substituents selected from C₁₋₄ alkoxy (eg methoxy or ethoxy). C₁₋₄alkyl (eg methyl, ethyl, n-propyl, i-propyl, n-butyl or t-butyl), andhalogen (eg bromine or chlorine);

R² represents a C₁₋₄ alkyl group (preferably methyl or ethyl);

R³ represents hydrogen or methyl; and

Y--X represents the group --CH₂ O--;

and salts and physiologically functional derivatives thereof.

Particularly preferred compounds according to the present invention onthe basis of their activity, include:

methylN-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,

methylN-[6-(3,5-dimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,

methyl N-[2,5-dimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,

methyl N-[6-(1-naphthylmethyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,

methyl N-[6-(3-methylbenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,

methylN-[6-(2,3-dimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,

methylN-[6-(2,5-dimethylbenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,

ethylN-[6-(2,5-dimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,

ethylN-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,

methylN-methyl-N-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,

methylN-[6-(2-bromo-3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,

n-propylN-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,and

n-butylN-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,

2-methoxyethylN-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,

methylN-[6-(3,5-dimethoxy-4-ethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,

and physiologically functional derivatives thereof.

Compounds of the present invention have cytotoxic activity, i.e. theyare toxic to certain living cells which are detrimental to mammals, forexample tumour cells.

The antitumour acitvity of compounds of general formula (I) has beendemonstrated in a number of standard tests both in vitro and in vivo,primarily by activity against murine leukaemic cell lines e.g. P388.

Thus, compounds of general formula (I) have been found to exhibit potentanti-tumour activity against P388 in vitro in proliferative assays andin the more stringent colony-forming assays. In vivo, compounds of theinvention effected a reduction in the number of tumour cells in micebearing ascitic P388/O leukaemia tumours, and a consequent increase insurvival duration as compared to an untreated tumour bearing controlgroup.

Activity in the above standard in vivo tumour test has been reported tobe indicative of antitumour activity in man (A. Goldin et al, in Methodsin Cancer Research, ed. V.T. DeVita Jr. and H. Busch, 16 198-199,Academic Press N.Y. 1979).

Compounds of the invention have also been found to interfere withtubulin function, as evidenced by inhibition of tubulin polymerisationin vitro.

It has previously been reported that compounds which act as microtubuleinhibitors appear to block the directional migration of tumour cells. Itis therefore believed that compounds of the present invention will haveanti-invasive and antimetastatic properties.

It addition to the above described properties, several preferredcompounds of the invention have been found to exhibit activity against avariety of human tumour cell lines in vitro (DLD-1 human coloncarcinoma, WiDr human colon adenocarcinoma, HCT-116 human coloncarcinoma and A549 human lung carcinoma) indicating that the compoundshave broad spectrum antitumour activity.

A particularly preferred compound on the basis of its activity is methylN-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,and physiologically functional derivatives thereof. This compound hasfurther been found to exhibit good activity against various murinetumours in vivo (B16 melanoma and L1210 leukaemia). In addition it hasalso been found advantageously to exhibit good activity in vivo againststrains of P388 which are resistant to the major clinically usedanti-tumour agents including cyclophosphamide, methotrexate, actinomycinD, vincristine, adriamycin, 5-fluorouracil, cis-platinum,bis-chloronitrosourea and amsacrine. It is believed that the adriamycin,vincristine and actinomycin D-resistant tumours are in fact resistant toa wide variety of antitumour drugs.

Without wishing to be bound by theory it is believed that certaincompounds according to the invention act as pro-drugs. Thus, compoundsof formula (I) wherein R³ is an alkyl group have higher activity in vivothan would be expected on the basis of their in vitro activity, and itis believed that they are converted in vivo into a compound of formula(I) wherein R¹ is hydrogen.

According to a further aspect, the present invention also provides aprocess for preparing compounds of general formula (I), which processcomprises:

(A) reaction of a pyridazine derivative of general formula (II) ##STR3##(wherein R¹, and X and Y are as hereinbefore defined) with a compound ofgeneral formula (III): ##STR4## (wherein R² and R³ are as hereinbeforedefined and Z represents a halogen atom e.g. a chlorine or bromineatom).

(B) reaction of a pyridazine derivative of general formula (IV) ##STR5##(wherein R² and R³ are as hereinbefore defined and Z¹ represents aleaving group such as a halogen atom or sulphonate group, e.g. methanesulphonate or p-toluene sulphonate) with a compound of general formula(V)

    R.sup.1 CH.sub.2 X.sup.1 H                                 (V)

(wherein R¹ is as hereinbefore defined and X¹ represents an oxygen orsulphur atom or a group NR⁴ as hereinbefore defined);

(C) reaction of a compound of formula (VI) ##STR6## with an appropriatealcohol R² OH

(D) reaction of a compound of formula (VII) ##STR7## with a reagentserving to introduce the group --CO₂ R²

(E) conversion of one compound of formula (I) into another compound offormula (I) for example by exchanging one esterifying group R² for adifferent esterifying group R² ; or by alkylation of a compound offormula (I) wherein R³ represents hydrogen; followed if desired and/orappropriate by salt formation.

General process (A) may conveniently be effected in an aprotic solvent,such as dimethylformamide, 1,3-dimethylimidazolidinone, orhexamethylphosphoramide, and at a non-extreme temperature, for exampleat between 50°-120° C.

Compounds of general formula (II) wherein X represents an oxygen orsulphur atom or a group NR⁴ may be prepared by reaction of anappropriate alcohol, thiol or amine of formula (V) as defined above witha compound of formula (VIII): ##STR8## (wherein Z¹ is as hereinbeforedefined).

The reaction will generally be conducted in the presence of a base, suchas potassium t-butoxide in a solvent such as dimethoxyethane.Alternative bases and solvents which may be employed in this reactioninclude sodium hydride in an aprotic solvent such as dimethylformamideor dimethyl sulphoxide, and sodium methoxide or ethoxide in an alcoholsuch as methanol or ethanol, or an aprotic solvent such as thosementioned hereinabove.

Compounds of formula (II) wherein X and Y together represent the group--CH═CH-- may be prepared from a compound of formula (IX) by successivereactions with a halogenating agent such as phosphorous trichloride andammonia. ##STR9##

Compounds of formula (IX) may be prepared by reacting an appropriatearylaldehyde R¹ CHO with 3-oxopentanoic acid (laevulinic acid) in thepresence of a base in aqueous alcohol followed by reaction withhydrazine under acidic conditions to give a compound of formula (X):##STR10## which may be dehydrogenated e.g. using selenium dioxide in analcohol e.g. ethanol to give a compound of formula (IX).

When it is desired to prepare compounds of formula (II) wherein X and Yare both methylene groups the ethenyl moiety in the compound of formula(IX) or (X) may first be reduced, for example by catalytic hydrogenationusing e.g. palladium on charcoal.

Compounds of formula (III) may be prepared by reaction of thecorresponding haloacetamide of formula (XI): ##STR11## with oxalylchloride, and an alcohol R² OH, according to methods well known in theart.

Alcohols of general formula (V) may be prepared from the correspondingcarboxylic acids or carboxaldehydes using standard procedures, e.g. byreduction with sodium borohydride in a solvent such as methanol orethanol, or with lithium aluminium hydride in a solvent such as diethylether or tetrahydrofuran.

A thiol of general formula (V) may be prepared from the correspondinghalide R¹ CH₂ Z³ (wherein Z³ is a halogen atom) by reaction withthiourea in a solvent such as ethanol, to give the correspondingisothiouronium salt, and subsequent hydrolysis e.g. with sodiumhydroxide solution.

Amines of general formula (V) may be prepared in conventional manner, byreaction of a corresponding halide with ammonia.

Reaction of a compound of general formula (IV) with a compound ofgeneral formula (V) according to process (B) will generally be effectedin the presence of a base. Suitable bases include alkali metal alkoxidessuch as sodium or potassium methoxide, ethoxide or t-butoxide. Thereaction may be conveniently carried out in a solvent, such asdimethoxyethane; an alcohol e.g. methanol or ethanol, or an aproticsolvent such as dimethylformamide or dimethylsulphoxide.

Compounds of general formula (IV) may be prepared by reacting a compoundof formula (VII) with a compound of formula (III) in an analogous mannerto general process (A) described above.

General process (C) may be effected by heating a compound of formula(VI) to a temperature in the range 80° to 150° C., optionally in thepresence of a solvent, and reacting with an alcohol R² OH.

Suitable solvents include inert organic solvents such as hydrocarbonse.g. benzene or toluene. Alternatively the alcohol R² OH may itself actas the solvent.

It is believed that process (C) proceeds via an intermediate isocyanatederivative of formula (XII) ##STR12##

Acyl-azide derivatives of formula (VI) may be prepared from thecorresponding carboxylic acids by formation of an activated acidderivative, (e.g. an acid halide such as an acid chloride formed byreaction with a halogenating agent such as oxalyl chloride, thionylchloride or phosphorus pentachloride) followed by reaction with an azidee.g. an alkali metal azide, conveniently in an aqueous ether solutione.g. aqueous dioxan. The carboxylic acid derivatives corresponding tocompounds (VI) may themselves be prepared by reacting a compound offormula (II) with ethyl bromopyruvate using analogous conditions togeneral process (A) above, to give an ester, followed by hydrolysis togive the desired acid.

In process (D) a reagent serving to introduce the group --CO₂ R² may bethe corresponding haloformate, e.g. an alkylhaloformate such as methyl-or ethyl-chloroformate. Compounds of formula (VII) may themselves beprepared from a compound of formula (I) by removal of a group --CO₂ R²,(preferably a labile group such as t-butoxycarbonyl) under acidconditions (using e.g. an optionally halogenated carboxylic acid such asformic, chloroformic or trifluoacetic acid), optionally in the presenceof a solvent, e.g. a halogenated hydrocarbon such as dichloromethane.Thus, in a particular embodiment of process (D) one compound of formula(I) may be converted into a different compound of formula (I), byremoval of one group --CO₂ R² and reaction to introduce a differentgroup --CO₂ R² as described above.

Conversion of a compound of formula (I) into a different compound offormula (I) according to general process (E) may be achieved for exampleby replacing an esterifying group R² in the compound of formula (I) by adifferent group R² by heating a compound (I) with an appropriate alcoholin the presence of a base, for example an alkali metal alkoxide such aspotassium t-butoxide, at a temperature in the range 50° to 180° C.Whilst such ester exchange may be carried out as a separate reactionstep, it may also conveniently be effected during the course of thereaction between a compound of formula (IV) with a compound (V)according to general process (B).

Interconversion according to process (E) may also be achieved byalkylation of a compound wherein R³ is a hydrogen atom, to provide acompound wherein R³ is an alkyl group. Alkylation may be effected inconventional manner, for example using an alkyl halide, e.g. methyl orethyl iodide, in the presence of a base, e.g. sodium hydride.

Those intermediates of formulae (II) to (XI) which are novel form afurther aspect of the present invention. Preferred intermediates arethose of formulae (II), (IV) and (VI).

The compounds of the present invention are useful for the treatment oftumours. They may be employed in treating various forms of cancerincluding leukaemias, lymphomas, sarcomas and solid tumours.

The invention thus further provides a method for the treatment oftumours in animals, including mammals, especially humans, whichcomprises the administration of a clinically useful amount of compoundof formula (I) or a pharmaceutically acceptable salt or physiologicallyfunctional derivative in a pharmaceutically useful form, once or severaltimes a day or in any other appropriate schedule, orally, rectally,parenterally, or applied topically.

In addition, there is provided as a further, or alternative, aspect ofthe invention, a compound of formula (I) or a pharmaceuticallyacceptable salt or physiologically functional derivative thereof for usein therapy, for example as an antitumour agent.

The amount of compound of formula (I) required to be effective as acytotoxic agent will, of course, vary and is ultimately at thediscretion of the medical or veterinary practitioner. The factors to beconsidered include the condition being treated, the route ofadministration, and nature of the formulation, the mammal's body weight,surface area, age and general condition, and the particular compound tobe administered. A suitable effective antitumour does is in the range ofabout 0.01 to about 120 mg/kg body weight, e.g. 0.1 to about 120 mg/kgbody weight, preferably in the range of about 0.1 to 50 mg/kg, forexample 0.5to 5 mg/kg. The total daily dose may be given as a singledose, multiple doses, e.g., two to six times per day or by intravenousinfusion for selected duration. For example, for a 75 kg mammal, thedose range would be about 8 to 9000 mg per day, and a typical dose couldbe about 50 mg per day. If discrete muliple doses are indicatedtreatment might typically be 15 mg of a compound of formula (I) given upto 4 time per day.

Whilst it is possible for the active compound to be administered alone,it is preferable to present the active compound in a pharmaceuticalformulation. Formulations of the present invention, for medical use,comprise a compound of formula (I) or a salt thereof together with oneor more pharmaceutically acceptable carriers and optinally othertherapeutic ingredients. The carrier(s) should be pharmaceuticallyacceptable in the sense of being compatible with the other ingredientsof the formulation and not deleterious to the recipient thereof.

The present invention, therefore, further provides a pharmaceuticalformulation comprising a compound of formula (I) or a pharmaceuticallyacceptable salt or physiologically functional derivative therof togetherwith a pharmaceutically acceptable carrier therefor.

There is also provided a method for the preparation of a pharmaceuticalformulation comprising bringing into association a compound of formula(I) or a pharmaceutically acceptable salt or physiologically functionalderivative thereof, and a pharmaceutically acceptable carrier therefor.

Formulations according to the present invention include those suitablefor oral, topical, rectal or parenteral (including subcutaneous,intramuscular and intravenous) administration. Preferred formulationsare those suitable for oral or parenteral administration.

The formulations may conveniently be presented in unit dosage forms andmay be prepared by any of the methods well known in the art of pharmacy.All methods include the step of bringing the active compound intoassociation with a carrier which constitutes one or more accessoryingredients. In general, the formulations are prepared by uniformly andintimately bringing the active compound into association with a liquidcarrier or a finely divided solid carrier or both and then, ifnecessary, shaping the product into desired formulations.

Formulations of the present invention suitable for oral administrationmay be presented as discrete units such as capsules, cachets, tablets orlozenges, each containing a predetermined amount of the active compound;as a powder or granules; or a solution or suspension in an aqueous ornon-aqueous liquid such as a syrup, an elixir, an emulsion or a draught.

A tablet may be made by compression or moulding, optionally with one ormore accessory ingredients. Compressed tablets may be prepared bycompressing in a suitable machine the active compound in a free-flowingform such as a powder or granules, optionally mixed with a binder,lubricant, inert diluent, surface active or dispersing agent. Mouldedtablets may be made by moulding in a suitable machine a mixture of thepowdered active compound with any suitable carrier.

A syrup may be made by adding the active compound to a concentrated,aqueous solution of a sugar, for example sucrose, to which may also beadded any accessory ingredients. Such accessory ingredient(s) mayinclude flavourings, an agent to retard crystallization of the sugar oran agent to increase the solubility of any other ingredients, such as apolyhydric alcohol for example glycerol or sorbitol.

Formulations for rectal administration may be presented as a suppositorywith a conventional carrier such as cocoa butter.

Formulations suitable for parenteral administration convenientlycomprise a sterile aqueous preparation of the active compound which ispreferably isotonic with the blood of the recipient. Such formulationssuitably comprise a solution of a pharmaceutically and pharmacologicallyacceptable acid addition salt of a compound of the formula (I) that isisotonic with the blood of the recipient.

Useful formulations also comprise concentrated solutions or solidscontaining the compound of formula (I) which upon dilution with anappropriate solvent give a solution for parenteral administration asabove.

In addition to the aforementioned ingredients, the formulations of thisinvention may further include one or more accessory ingredient(s)selected from diluents, buffers, flavouring agents, binders, surfaceactive agents, thickeners, lubricants, preservatives (includingantioxidants) and the like.

In a further aspect the present invention provides the use of a compoundof formula (I) or a pharmaceutically acceptable salt or physiologicallyfunctional derivative thereof for the manufacture of a medicament forthe treatment of tumours.

The invention will now be illustrated by the following non-limitingExamples.

All temperatures are in degrees Celcius (°C.).

Proton nuclear magnetic resonance spectra were obtained on a BrukerAH200 FT NMR or Bruker HFX90 FT NMR machine.

The following abbreviations are used in the preparations and Examples

DME--dimethoxyethane

DMEU--1,3-dimethyl-2-imidazolidone.

LAH--lithium aluminumum hydride.

PREPARATION OF INTERMEDIATES Intermediate 13-Amino-6-(3,4,5-trimethoxybenzyloxy)pyridazine

3,4,5-Trimethoxybenzyl alcohol (Aldrich 19.82 g, 0.1 mol), dissolved inDME (20 ml), was added over 15 mins to a suspension of potassiumt-butoxide (11.22 g, 0.1 mol) in DME (80 ml) with stirring under N₂ andcooling in an ice-bath. After 0.5 h the mixture was treated with3-amino-6-chloropyridazine (Helv. Chim. Acta. 1954, 37, 121, J. Druey,Kd. Meier and K. Eichenberger) (12.95 g, 0.1 mol) and after 1.5 h washeated under reflux for 3 h. The mixture was cooled and filtered and thefiltered solid washed with ether. The filtrate was evaporated in vacuoto give an oil which was partitioned between ethyl acetate and water.The organic phase was washed with water, dried (Na₂ SO₄) and evaporatedto give an oil (A) which was chromatographed on silica gel eluting with5% methanol-chloroform. Eluted fractions were combined to give an oil(B) which was triturated with chloroform and di-isopropyl ether to yieldthe title compound as an off-white solid (9.44 g), m.p.=142°-4°; Nmr. δH(CDCl₃) 6.87 (1H, J_(AB) 8.8 Hz 5-H), 6.78 (1H, J_(AB) 8.8 Hz, 4-H),6.72 (2H, s, PhH), 5.38 (2H, s, CH₂), 4.45 (2H, br, s, NH₂) 3.87 (6H, s,OMe) and 3.84 (3H, s, OMe).

Intermediate 2 3-Amino-6-(2,5-dimethoxybenzyloxy)pyridazine

2,5-Dimethoxybenzyl alcohol (30.6 g, 0.182 mol) in DME (20 ml) was addedto potassium t-butoxide (20.38 g, 0.182 mol) in DME (60 ml) withstirring under N₂ and cooling in an ice-bath. After 0.5 h, the mixturewas treated with 3-amino-6-chloropyridazine and after 1.5 hours washeated under reflux for 5 h, then cooled and filtered. The filtrate wasevaporated in vacuo and partitioned between ethyl acetate and water. Theorganic phase was washed with water, dried (Na₂ SO₄) and evaporated togive a solid (A) which was recrystallised from toluene to give a solid(B). This was chromatographed on silica gel eluting with 5%methanol-chloroform to yield the title compound as a white solid (27 g),m.p.=94°-94.5°, Nmr δ_(H) (CDCl₃) 7.05 (1H, m, PhH), 6.90-6.73 (4H, m,ArH), 5.42 (2H, s, CH₂), 4.5 (2H, brs, NH₂) and, 3.78 and 3.75 (6H, s,OMe).

Intermediates 3 to 12

The following compounds were prepared from the appropriate alcohol bythe general procedure described for Intermediates 1 and 2:

(3) 3-Amino-6-(1-naphthylmethyloxy)pyridazine, m.p. 143°-144° , Nmrδ_(H) (d₆ -DMSO) 8.00 (3H, m, napth H), 7.55 (4H, m, napth H), 6.97 (1H,J_(AB) 8.8 Hz 4-H), 6.89 (1H, J_(AB) 8.8 Hz 5-H), 6.0 (2H, s, CH₂) and5.80 (2H, s, NH₂). (From 1-naphthylmethanol, Aldrich)

(4) 3-Amino-6-(3-methoxybenzyloxy)pyridazine, m.p. 55°-60°, Nmr δ_(H)(d₆ -DMSO) 7.38 (1H, dd, J8-4 Hz, PhH), 7.13-6.89 (5H, m, ArH), 6.05(2H, s, NH₂), 5.35 (2H, s, CH₂) and 3.82 (3H, s, OMe).

(5) 3-Amino-6-(3,5-dimethoxybenzyloxy)pyridazine, m.p. 89°-92°, Nmrδ_(H) (d₆ -DMSO) 6.88 (1H, J_(AB) 8.8 Hz, 5-H), 6.75 (1H, J_(AB) 8.8 Hz,4-H), 6.62 (2H, d, 2'-H and 6'-H), 6.42 (1H, t, 4'-H), 5.35 (2H, s,CH₂), 4.53 (2H, br.s, NH₂) and 3.75 (6H, s, OMe).

(6) 3-Amino-6-(3-Methylbenzyloxy)pyridazine, Nmr δ_(H) (d₆ -DMSO)7.40-7.10 (4H, m, PhH), 6.90 (2H, J_(AB) 8.8 Hz, 4-H and 5-H), 5.91 (2H,br.s, NH₂), 5.17 (2H, s, CH₂) and 2.31 (3H, s, Me); M/Z 215 (M⁺, 30%),198 (9), 123 (23), 111 (31) and 105 (100).

(7) 3-Amino-6-(3-dimethylaminobenzyloxy)pyridazine, m.p. 127°-129°, Nmrδ_(H) (d₆ -DMSO) 7.25 (1H, t, 5'-H), 7.00 (1H, J_(AB) 8.8 Hz, 4-H), 6.92(1H, J_(AB) 8.8 Hz, 5-H), 6.90-6.70 (3H, m, 2'-, 4'- and 6'-H), 5.95(2H, s, CH₂), 5.30 (2H, br.s, NH₂) and 2.98 (6H, s, NMe₂). (From3-dimethylaminobenzylalcohol, prepared by LAH reduction of3-dimethylaminobenzoic acid, Aldrich)

(8) 3-Amino-6-(2-methoxybenzyloxy)pyridazine, m.p. 166°-168°, Nmr δ_(H)(CDCl₃) 7.8 (1H, dd, J 6.7 and 2.2 Hz, PhH), 7.30 (1H, dd, J 6.6 and 2.2Hz, PhH), 6.98 (1H, dt, J 6.6 Hz, PhH), 6.92 (1H, d, J 6.6 Hz, PhH),6.90 (1H, J_(AB) 8.8 Hz, 5-H), 6.78 (1H, J_(AB) 8.8 Hz, 4-H), 5.5 (2H,s, CH₂), 4.42 (2H, br.s, NH₂) and 3.87 (3H, s, OMe).

(9)3-Amino-6-[3,5-dimethoxy(4-methoxyethoxymethoxy)benzyloxy]pyridazine,m.p. 110°-114°, Nmr, δ_(H) (CDCl₃) 6.88 (1H, J_(AB) 8.8 Hz, 5-H), 6.78(1H, J_(AB) 8.8 Hz, 4-H), 6.7 (2H, 5,2'- and 6'-H), 5.35 (2H, s, CH₂),5.2 (2H, s, CH₂), 4.49 (2H, br.s, NH₂), 4.05 (2H, m, CH₂) 3.85 (6H, s,OMe), 3.61-3.51 (2H, m, CH₂) and 3.35 (3H, s, OMe).

(10) 3-Amino-6-(3-chlorobenzyloxy)pyridazine, Nmr δ_(H) (d₆ -DMSO)7.51-7.32 (4H, m, PhH), 6.91 (2H, J_(AB) 8.8 Hz, 4H and 5-H), 5.92 (2H,br.s, NH₂) and 5.34 (2H, s, CH₂); M/Z 235 (M⁺, 68%), 218 (10), 125 (65)and 97 (100).

(11) 3-Amino-6-(2-thienylmethyloxy)pyridazine, m.p. 101°-103°, Nmr δ_(H)(d₆ -DMSO), 7.52 (1H, d, 5'-H), 7.20 (1H, d, 3'-H), 7.02 (1H, dd, 4'-H),6.94 and 6.85 (2H, J_(AB) 8.8 Hz, 4-H and 5-H), 5.95 (2-H, s, CH₂) and5.50 (2H, s, NH₂).

(12) 3-Amino-6-(3,4,5-trimethoxybenzylthio)pyridazine was preparedaccording to the method described for Intermediates 1 and 2 using3,4,5-trimethoxybenzylthiol and 3-amino-6-chloro pyridazine to give theproduct, m.p. 143°-146°, Nmr δ_(H) (CDCl₃) 7.07 and 6.63 (2H, J_(AB) 8.8Hz, 4-H and 5-H), 6.66 (2H, s, PhH) 4.63 (2H, br.s, NH₂), 4.44 (2H, s,CH₂), 3.85 (6H, s, OMe) and 3.84 (3H, s, OMe).

Intermediate 13 2-Methoxyethyl N-chloroacetylcarbamate

The procedure described by R. J. Bochis et. al., J. Med Chem 1978, 21,235 was followed to yield the title compound m.p. 97°-99°, Nmr δ_(H) (d₆-DMSO) 11.07 (1H, br.s, NH), 4.56 (2 h, s, ClCH₂), 4.28 (2H, m,CO.OCH₂), 3.62 (2H, m, CH₂ OMe) and 3.34 (3H, s, Me).

The following intermediates of formula (III) are known from theliterature references indicated:

    ______________________________________                                        Z--CH.sub.2 CONHCO.sub.2 R.sup.2                                              Intermediate                    Literature                                    No.        Z        R.sup.2     ref.                                          ______________________________________                                        14         Cl       CH.sub.3    a                                             15         Br       t-Butyl     b                                             16         Cl       --CH.sub.2 CH.sub.3                                                                       c                                             17         Cl       --CH.sub.2 CH.sub.2 CH.sub.3                                                              c                                             18         Cl       --(CH.sub.2).sub.3 CH.sub.3                                                               c                                             19         Cl                                                                 iso-propyl d                                                                  ______________________________________                                    

(a) R. J. Bochis et. al J. Med. Chem 1978, 21 235.

(b) N. J. Leonard and K. A. Cruikshank--J. Org. Chem, 1985, 50 2480

(c) M. Pianka and D. J. Pelton J. Chem. Soc. 1960, 983

(d) G. I. Derkach and V. P. Belaya, Zh Obsch. Khim, 1966, 36, 1942.

Intermediates 20-32

The following compounds were prepared by the general procedure describedfor Intermediates (1) and (2), using the appropriate alcohol as startingmaterial.

Intermediate 20 3-Amino-6-(2,3-dimethoxybenzyloxy)pyridazine

From 2,3-dimethoxybenzylalcohol (Aldrich) to give the title compound mp.103°-106°, NMR δH (CDCl₃) 7.12-7.05 (2H, m, 5' and 6'H); 6.91 (1H, m,4'H), to 6.85 (1H, J_(AB) 9 Hz,5H), 6.77 (1H, J_(AB) 9 Hz, 4H); 5.50(2H, s, ArCH₂); 4.50 (2H, brs, NH₂) and 3.89 (6H, s, OCH₃).

Intermediate 21 3-Amino-6-(3,5-dimethoxy-4-ethoxybenzylozy)pyridazine

From 3,5-dimethoxy-4-ethoxybenzylalcohol to give the title compound m.p.161°-171°, NMR δH (CDCl₃) 6.89 (1H, J_(AB) 8.8 Hz, 5H); 6.79 (1H, J_(AB)8.8 Hz, 4H); 6.70 (2H, s, ArH); 5.38 (2H, s, ArCH₂); 4.48 (2H, brs,NH₂); 4.06 (2H, q, J 7 Hz, CH₂ CH₃); 3.88 (6H, s, OCH₃) and 1.38 (3H, t,J 7 Hz, CH₂ CH₃).

3,5-Dimethoxy-4-ethoxybenzylalcohol was prepared as follows:

a) 3,5-Dimethoxy-4-ethoxybenzaldehyde

A mixture of syringaldehye (50 g, 0.275 mole), ethyl iodide (85.5 g,0.55 mol) and potassium carbonate (151.7 g. 1.09 mol) in DMF (60 ml) wasstirred and heated at 60°-70° for 6 h. The mixture was cooled andevaporated in vacuo then treated with water and extracted with diethylether. The extracts were dried (Na₂ SO₄) and evaporated to give thetitle compound (59 g) as a white solid, pure by tlc, and used withoutfurther purification.

b) 3,5-Dimethoxy-4-ethoxybenzlyalcohol

The product form the previous reaction (59 g, 0.28 mol) was dissolved inmethanol-ethanol (600 ml, 1:1) and treated with sodium borohydride (10.8g, 0.285 mol) portionwise over 1 h. The mixture was stirred for 24 h atambient temperature then treated slowly with water (50 ml) to provide aprecipitate. The mixture was evaporated to remove organic solvents,treated with water (300 ml) and extracted with chloroform. The extractswere dried (Na₂ SO₄) and evaporated to give a white solid which wasrecrystallised from ether to give the title compound (26 g ) as whiteneedles.

Intermediate 22 3-Amino-6-(2-t-butylbenzyloxy)pyridazine

From 2-t-butylbenzyl alcohol to give title compound mp. 147°-9° δH(DMSO) 7.4 (2H, m, ArH), 7.28 (2H, m, ArH), 6.9 (1H, J_(AB), 8 Hz, 4H),6.85 (1H, J_(AB), 8 Hz, 5H), 6.0 (2H, brs, NH₂), 5.5 (2H, s, CH₂), 1.4(9H, s, Me₃). (Acohol prepared by LAH reduction of 2-t-butylbenzoicacid; M. Crawford and F. H. C. Stewart, J. Chem. Soc., 1952, 4444).

Intermediate 23 3-Amino-6-(2-ethylbenzyloxy)pyridazine

From 2-ethylbenzylalcohol.

Alcohol prepared form 2-ethylbenzoic acid (M. Crawford and F. H. C.Stewart, J. Chem. Soc. 1952, 4444) by reduction with LAH.

Intermediate 24 3-Amino-6-(2,5-dimethylbenzyloxy)pyridazine

From 2,5-dimethylbenzylalcohol to give title compound mp. 109°-111° C.

Alcohol prepared by LAH reduction of 2,5-dimethylbenzoic acid (Aldrich).

Intermediate 25 3-Amino-6-(3,4,5-trimethylbenzyloxy)pyridazine

From 3,4,5-trimethylbenzylalcohol.

Alcohol prepared by LAH reduction of 3,4,5-trimethylbenzoic acid (G. H.Kosolapoff, J.Am. Chem. Soc. 69, 1652, 1947).

Intermediate 26 3-Amino-6-(2-phenylbenzyloxy)pyridazine

From 2-Phenylbenzylalcohol.

Alcohol prepared by LAH reduction of 2-phenylbenzoic acid (Aldrich).

Intermediate 27 3-Amino-6-(3-diethylaminobenzyloxy)pyridazine

From 3-diethylaminobenzylalcohol to give title compound mp. 115°-118° C.

δH (DMSO), 7.15 (1H, t, 5'H), 6.95 (1H, J_(AB) , 8 Hz, 4H), 6.85 (1H,J_(AB) , 8 Hz, 5H), 6.75 (1H, brs, 2'H), 6.65 (2H, m, 4'H+6'H), 5.9 (2H,s, NH₂), 5.25 (2H, s, CH₂ O), 3.3 (4H, quad, 2×CH₂ N), 1.05 (6H, t,2×Me).

Alcohol prepared by LAH reduction of 3-diethylaminobenzoic acid (P.Griess, Chem. Ber., 5 1041, 1872)

Intermediate 28 3-Amino-6-(3-methylaminobenzyloxy)pyridazine

From 3-methylaminobenzylalcohol to give the title compound as a gum.

δH (DMSO) 7.1 (1H, t, 5'H), 6.95 (1H, J_(AB) , 8 Hz, 4H), 6.85 (1H,J_(AB) , 8 Hz, 5H), 6.6 (2H, m, 2 ArH), 6.45 (1H, d, ArH), 5.95 (2H, s,NH₂), 5.65 (1H, brs, NH), 5.2 (2H, s, CH₂ O), 2.65 (3H, s, MeN).

Alcohol prepared by LAH reduction of 3-methylaminobenzoic acid (J.Houben and W. Brassert. Chem. Ber., 43 209, 1910)

Intermediate 29 3-Amino-6-(3-methoxy-1-naphthylmethoxy)pyridazine

From 3-methoxy-1-naphthylmethanol to give the title compound mp.167°-170° C.

δH (DMSO), 7.95 (2H, 2 d, 2 ArH), 7.40 (3H, m, 3 ArH), 7.30 (1H, s,2'H), 7.0 (1H, J_(AB) , 8 Hz, 4H), 6.90 (1H, J_(AB) , 8 Hz, 5H), 6.00(2H, s, NH₂), 5.75 (2H, s, CH₂ O), 3.90 (3H, s, OMe).

Alcohol prepared by LAH reduction of 3-methoxy-1-naphthoic acid (R.Lesser and G. Gad, Chem. Ber., 58B, 2551-9, 1925)

Intermediate 30 3-Amino-6-[2-(3,4,5-trimethoxyphenyl)ethoxyl]pyridazine

From 2-(3,4,5-trimethoxyphenyl)ethanol to give an oil.

δH (DMSO), 6.95 (1H, J_(AB), 8 Hz, 4H), 6.90 (1H, J_(AB), 8 Hz, 5H),6.60 (2H, s, 2 ArH) 6.25 (2H, brs, NH₂), 4.45 (2H, t, CH₂ O), 3.75 (6H,s, 3 MeO and 5 MeO), 3.58 (3H, s, 4 MeO), 3.0 (2H, t, CH₂).

Alcohol prepared by LAH reduction of 3,4,5-trimethoxyphenylacetic acid(Aldrich).

Intermediate 31 3-Amino-6-(2-pyridylmethoxy)pyridazine

From 2-pyridylmethanol (Aldrich) to give the title compound mp.114°-115°. Nmr δH (d₆ -DMSO), 8.65 (1H, d, 6'-H), 7.85 (1H, tr of d,5'-H), 7.55 (1H, d, 3'-H), 7.45 (1H, m, 4'-H), 7.10 (1H, J_(AB) 8.8 Hz,4-H), 6.95 (1H, J_(AB) 8.8 Hz, 5-H), 6.05 (2H, s, NH₂), 5.45 (2H, s,CH₂).

Intermediate 32 3-Amino-6-(2-furfuryloxy)pyridzaine

From furfurylalcohol to give the title compound mp. 96°-99° . Nmr δH (d₆-DMSO), 7.70 (1H, d, 5'-H), 6.90 (1H, J_(AB) 8.8H_(z), 4-H), 6.85 (1H,J_(AB) 8.8H_(z), 5-H), 6.60 (1H, d, 4'-H), 6.50 (1H, s, 3'-H), 5.95 (2H,s, NH₂), 5.30 (2H, s, CH₂).

EXAMPLE 1 MethylN-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2]pyridazin-2-yl]carbamate

Intermediate 1 (29.1 g, 0.1 mol), and methyl N-chloroacetylcarbamate(15.15 g, 0.1 mol) were heated at 100° for 3 h with stirring under N₂ indry 1,3-dimethyl-2-imidazolidinone (DMEU) (100 ml). The mixture wascooled, poured onto iced sodium bicarbonate solution and filtered togive a solid which was washed with water. The solid was dissolved in 5%methanol-chloroform and eluted through florosil. Evaporation gave asolid which was recrystallised from dimethylformamide and water to givethe title compound as a white powder (14 g), m.p. 217°-220°, Nmr δ_(H)(d₆ -DMSO) 10.36 (1H, br.s, NH), 7.87 (1H, J_(AB) 8.8 Hz, 8-H), 7.85(1H, s, 3-H), 6.87 (1H, J_(AB) 8.8 Hz, 7-H), 6.85 (2H, s, PhH), 5.25(2H, s, CH₂), 3.79, 3.70 and 3.56 (2H, s, OMe).

EXAMPLE 2 EthylN-[6-(2,5-Dimethoxybenzyloxy)imidazo[1,2-b)pyridazin-2-yl]carbamate

Intermediate 2 (2.61 g, 10 mmol), 2,6-lutidine (1.04 g, 10 mmol) andethyl N-chloroacetylcarbamate (1.66 g, 10 mmol) were heated at 100° for3 h with stirring under N₂ in dry DMEU (10 ml). The mixture was cooledand filtered and the solid washed with water and ether then passedthrough florosil, eluting with 5% methanol-chloroform. Evaporation ofthe eluate gave a solid which was recrystallised from dimethylformamideand water to give the title compound as a white powder (1.26 g), m.p.210°-211°, Nmr δ_(H) (d₆ -DMSO) 10.24 (1H, br.s, NH), 7.85 (2H, M, 3-H),7.10-6.86 (4H, m, 7-H and PhH), 5.27 (2H, s, CH₂ Ar), 4.17 (2H, q, J 6.6Hz, CH₂ CH₃), 3.78 and 3.73 (6H, s, OMe) and 1.27 (3H, t, J 6.6 Hz, CH₂CH₃).

EXAMPLE 3 MethylN-[6-(2,5-Dimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

Intermediate 2 (12.0 g, 0.046 mol), 2,6-lutidine (4.92 g, 0.046 mol) andmethyl N-chloroacetyl carbamate (6.97 g, 0.046 mol) were heated withstirring under N₂ at 100° for 4 h in dry DMEU (46 ml). The mixture wasadded to iced-water and then filtered to give a solid which wasrecrystallised from dimethylformamide and water to give the titlecompound as a light brown powder (2.46 g), m.p. 228°-230°, Nmr δ_(H) (d₆-DMSO) 10.30 (1H, br.s, NH), 7.88 (1H, J_(AB) 8.8 Hz, 8-H), 7.85 (1H, s,3-H), 7.12-6.85 (4H, m, ArH), 5.32 (2H, s, CH₂), and 3.79, 3.72 and 3.69(9H, s, OMe).

EXAMPLES 4 TO 22

The following compounds were prepared by the general procedure describedin Examples 1-3 by reacting the 3-amino-6- substituted pyridazines withthe appropriate chloroacetylcarbamates.

(4) n-PropylN-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,m.p. 174°-175°, Nmr δ_(H) (d₆ -DMSO) 10.25 (1H, br.s, NH), 7.87 (1H,J_(AB) 8.8 Hz, 8-H), 7.85 (1H, s, 3-H) 6.87 (1H, J_(AB) 8.8 Hz, 7-H),6.85 (2H, s, PhH), 5.26 (2H, s, CH₂ Ar), 4.07 (2H, t, J 6 Hz, CH₂ CH₂CH₃), 3.80 (6H, s, OMe), 3.68 (3H, s, OMe), 1.55 (2H, dt, J 6 Hz, CH₂CH₂ CH₃) and 0.94 (3H, t, J 6 Hz, CH₂ CH₂ CH₃)

(5) n-ButylN-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2yl]carbamate,m.p. 185°-187°, Nmr δ_(H) (d₆ -DMSO) 10.23 (1H, br.s, NH), 7.85 (1H,J_(AB) 8.8 Hz, 8-H), 7.8 (1H, s, 3-H), 6.86 (1H, J_(AB) 8.8 Hz, 7-H),6.65 (2H, s, PhH), 5.27 (2H, s, CH₂ Ar), 4.12 (2H, t, J 6 Hz, CH₂ CH₂CH₂ CH₃), 3.80 (6H, s, OMe), 3.67 (3H, s, OMe), 1.61 (2H, m, CH₂ CH₂ CH₂CH₃), 1.38 (2H, m, CH₂ CH₂ CH₂ CH₃) and 0.92 (3H, t, J 6 Hz, CH₂ CH₂ CH₂CH₃).

(6) n-PropylN-[6-(2,5-dimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,m.p. 199°-200°, Nmr δ_(H) (d₆ -DMSO) 9.93 (1H, br.s, NH) 7.87 (2H, m,3-H and 8-H), 7.17-6.89 (4H, m, 7-H and PhH), 5.42 (2H, s, CH₂ Ar), 4.17(2H, t, J 6 Hz, CH₂ CH₂ CH₃), 3.85 and 3.80 (6H, s, OMe), 1.73 (2H, dt,J 6 Hz, CH₂ CH₂ CH₃) and 1.04 (3H, t, J 6 Hz, CH₂ CH₂ CH₃).

(7) EthylN-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,m.p. 204°-206°, Nmr δ_(H) (d₆ -DMSO) 10.25 (1H, br.s, NH), 7.85 (1H,J_(AB) 8.8 Hz, 8-H), 7.83 (1H, s, 3-H) 6.85 (1H, J_(AB) 8.8 Hz, 7-H),6.64 (2H, s, PhH), 5.27 (2H, s, CH₂ Ar), 4.15 (2H, q, J 6 Hz, CH₂ CH₃),3.28 (6H, s, OMe), 3.16 (3H, s, OMe) and 1.25 (3H, t, J 6 Hz, CH₂ CH₃).

(8) 2-MethoxyethylN-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,m.p. 183°-185°, Nmr δ_(H) (d₆ -DMSO) 10.36 (1H, br.s, NH), 7.85 (1H,J_(AB) 8.8 Hz, 8-H), 7.83 (1H, s, 3-H), 6.85 (1H, J_(AB) 8.8 hz, 7-H),6.84 (2H, s, PhH), 5.26 (2H, s, CH₂ Ar), 4.25 (2H, m, COCH₂), 3.79 (6H,s, OMe), 3.18 (3H, s, OMe) 3.08 (2H, m, CH₂ OMe) and 3.32 (3H, s, CH₂OMe).

(9) MethylN-[6-(1-Naphthylmethyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate, m.p.243°-246°, δH (d₆ DMSO) 10.05 (1H, br.s, NH), 8.25-7.55 (9H, m, napth Hand 3-H and 8-H), 6.92 (1H, J_(AB) 8.8 Hz, 7-H), 5.92 (2H, s, CH₂ and3.80 (3H, s, OMe).

(10) MethylN-[6-(2-Methoxybenzyloxy)imidazo[1,2-b]pyridazin-2yl]carbamate, m.p.241°-243°, δ_(H) (d₆ DMSO) 10.1 (1H, br.s, NH), 7.92 (1H, s, 3-H), 7.65(1H, J_(AB) 8.8 Hz, 8-H), 7.45 (1H, d, J 7 Hz, PhH), 7.35 (1H, dd, J 7Hz, PhH), 6.95 (2H, m, PhH), 6.72 (1H, J_(AB) 8.8 Hz, 7-H), 5.36 (2H, s,CH₂), 3.89 (3H, s, OMe), and 3.77 (3H, s, OMe).

(11) MethylN-[6-(3,5-Dimethoxybenzyloxy)imidazo[1,2-b)pyridazin-2-yl]carbamate,m.p. 236°-238°, δ_(H) (d₆ DMSO) 10.30 (1H, br.s, NH), 7.88 (1H, J_(AB),8.8 Hz, 8-H), 7.82 (1H, s, 3-H), 6.90 (1H, J_(AB) 8.8 Hz, 7-H), 6.66(2H, d, J 0.9 Hz, 2'-H and 6'-H), 6.46 (1H, t, J 0.9 Hz, 4'-H), 5.36(2H, s, CH₂), 3.78 (6H, s, OMe) and 3.70 (3H, s, OMe).

(12) MethylN-[6-(3-methylbenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate, m.p.205°-208°, Nmr δ_(H) (d₆ -DMSO) 9.95 (1H, br, s, NH), 7.85 (1H, s, 3-H),7.80 (1H, J_(AB) 8.8 Hz, 8-H), 7.30 (3H, m, 2'-H, 4'-H and 6'-H), 7.151H, m, 5'-H), 6.82 (1H, J_(AB) 8.8 Hz, 7-H), 5.80 (2H, s, CH₂), 3.72(3H, s, OMe) and 2.34 (3H, s, Me).

(13) t-ButylN-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,m.p. 191.5°-192.5°, Nmr δ_(H) (d₆ -DMSO) 9.95 (1H, br.s, NH), 7.85 (1H,J_(AB) 8.8 Hz, 8-H), 7.79 (1H, br.s, 3-H) 6.87 (1H, J_(AB) 8.8 Hz, 7-H)6.86 (2H, s, PhH), 5.25 (2H, s, CH₂), 3.79 (6H, s, OMe), 3.68 (3H, s,OMe) and 1.50 (9H, s, t-Bu).

(14) MethylN-[6-(3,4,5-trimethoxybenzylthio)imidazo[1,2-b]pyridazin-2-yl]carbamate,m.p. 221°-223°, Nmr δ_(H) (d₆ -DMSO) 10.51 (1H, br.s, NH), 8.11 (1H, s,3-H), 7.87 (1H, J_(AB) 8.8 Hz, 8-H), 7.17 (1H, J_(AB) 8.8 Hz, 7-H), 6.88(2H, s, PhH), 4.49 (2H, s, CH₂), 3.83 (6H, s, OMe) and 3.70 (3H, s,OMe).

(15) MethylN-[6-(dimethylaminobenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,m.p. 200°-203°, Nmr δ_(H) (d₆ -DMSO) 10.05 (1H, br.s, NH), 7.93 (1H, s,3-H), 7.90 (1H, J_(AB) 8.8 Hz, 8-H), 7.30 (1H, t, 5'-H), 6.95-6.80 (4H,m, 2'-H, 4'-H, 6'-H and 7-H), 5.40 (2H, s, CH₂), 3.78 (3H, s, MeO) and2.98 (6H, s, NMe₂)

(16) MethylN-[6-(3-Methoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate m.p.184°-189.5°, Nmr δ_(H) (CDCl₃) 10.55 (1H, br.s, NH), 8.02 (1H, br.s,3-H), 7.75 (1H, J_(AB) 8.8 Hz, 8-H), 7.32 (1H, dd, J 7.5 Hz, 5'-H), 7.07(2H, m, ArH), 6.88 (1H, dd, J 7.5 and 2 Hz, ArH), 6.70 (1H, J_(AB) 8.8Hz, 7-H), 5.34 (2H, s, CH₂), 3.88 and 3.83 (6H, s, OMe).

(17) Ethyl N-(6-benzyloxyimidazo[1,2-b]pyridazin-2-yl]carbamate,m.p.>211° (decomp), Nmr δ_(H) (d₆ -DMSO) 10.25 (1H, br.s, NH), 7.87 (1H,J_(AB) 8.8 Hz, 8-H), 7.72 (1H, s, 3-H), 7.57-7.37 (5H, m, Ph), 5.35 (2H,s, CH₂ Ar), 4.15 (2H, q, J6 Hz, CH₂ CH₃) and 1.27 (3H, t, J6 Hz, CH₂CH₃).

(18) Methyl N-(6-n-butylthioimidazo[1,2-b]pyridazin-2-yl]carbamate, m.p.170°-171°, Nmr δ_(H) (d₆ -DMSO) 10.40 (1H, br.s, NH), 7.94 (1H, s, 3H),7.76 (1H, J_(AB) 8.8 Hz, 8-H), 7.06 (1H, J_(AB) 8.8 Hz, 7-H), 3.72 (3H,s, OMe), 3.18 (2H, t, J 6 Hz, CH₂ S), 1.68 (2H, m, CH₂ CH₂ S), 1.44 (2H,m, CH₂ CH₂ CH₂ S) and 0.93 (3H, t, J 6 Hz, CH₃ CH₂ CH₂ S).

(19) Methyl N-(6-benzylthioimidazo[1,2-b]pyridazin-2-yl]carbamate, m.p.223°-225° (decomp), Nmr δ_(H) (d₆ -DMSO) 10.42 (1H, br,s, NH), 7.99 (1H,s, 3-H), 7.77 (1H, J_(AB) 8.8 Hz, 8-H), 7.52-7.20 (5H, m, Ph), 7.07 (1H,J_(AB) 8.8 Hz, 7-H), 4.45 (2H, s, CH₂) and 3.68 (3H, s, OMe).

(20) MethylN-[6-(3,5-dimethoxy-4-(methoxyethoxymethoxy)benzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,m.p. 149°-150°, Nmr δ_(H) (CDCl₃) 9.58 (1H, br.s, NH), 8.02 (1H, br.s,3-H), 7.75 (1H, J_(AB) 8.8 Hz, 8-H), 6.75 (1H, J_(AB) 8.8 Hz, 7-H), 6.70(2H, s, 2'-H and 6'-H), 5.29 (2H, s, CH₂), 5.18 (2H, s, CH₂), 4.08-3.91(2H, m, CH₂), 3.85 (9H, s, OMe), 3.6-3.45 (2H, m, CH₂) and 3.35 (3H, s,OMe).

(21) MethylN-[6-(3-chlorobenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate m.p.268°-270°, Nmr δ_(H) (d₆ -DMSO) 10.32 (1H, br.s, NH) 7.87 (1H, J_(AB)8.8 Hz, 8-H), 7.83 (1H, s, 3-H), 7.61 (1H, s, 2'-H), 7.53-7.41 (3H, m,PhH), 6.91 (1H, J_(AB) 8.8 Hz, 7-H) 5.38 (2H, s, CH₂) and 3.68 (3H, s,OMe).

(22) Methyl N-[6-(2-thienylmethylimidazo[1,2-b]pyridazin-2-yl]carbamate,m.p. 207°-209°, Nmr δ_(H) (d₆ -DMSO), 10.38 (1H, br.s, NH), 7.85 (1H, s,3-H), 7.82 (1H, J_(AB) 8.8 Hz, 8-H), 7.58 (1H, d, 5'-H), 7.30 (1H, d,3'-H), 7.05 (1H, t, 4'-H), 6.82 (1H, J_(AB) 8.8 Hz, 7-H), 5.56 (2H, s,CH₂) and 3.66 (3H, s, OMe).

EXAMPLE 232,2,2-Trifluoroethyl-N-[6(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazine-2-yl]carbamatea) Ethyl6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazine-2-carboxylate

Ethyl bromopyruvate (117 g, 0.6 mol) was added to3-amino-6-(3,4,5-trimethoxy)pyridazine (174.6 g, 0.6 mol) and2,6-lutidine (62.4 g, 0.6 mol) in dry DMF (600 ml) with stirring underN₂. The mixture was heated at 100° for 3 h, cooled and concentrated invacuo then treated with water and filtered to give a brown solid whichwas washed with water and ether. The solid was crystallised from DMF andwater to give the title compound as a crystalline solid (88 g), m.p.159°-163°, Nmr δ_(H) (CDCl₃) 8.31 (1H, s, 3H), 7.84 (1H, J_(AB) 8.8 Hz,8H), 6.82 (1H, J_(AB) 8.8 Hz, 7H), 6.70 (2H, s, ArH), 5.30 (2H, s, CH₂Ar), 4.45 (2H, q, J7 Hz, OCH₂ CH.sub. 3), 3.88 (6H, s, OCH₃), 3.86 (3H,s, OCH₃) and 1.44 (3H, t, J7 Hz, CH₃).

b) 6(3,4,5-Trimethoxybenzyloxy)imidazo[1,2,-b-]pyridazine-2-carboxylicacid

The product of stage (a) (1.94 g, 5 mmol) was heated under reflux withstirring with sodium hydroxide solution (1 ml, 10M, 10 mmol), water (9ml) and methanol (5 ml) for 20 min. The mixture was cooled and acidifiedwith dilute hydrochloric acid and filtered to give a solid which wasdried at 60° in vacuo to give the title compound as a powder (1.5 g),m.p. 224°-226° (decomp), Nmr δ_(H) (d₆ -DMSO) 856 (1H, s, 3H), 8.07 (1H,J_(AB) 8.8 Hz, 8H), 7.05 (1H, J_(AB) 8.8 Hz, 7H) 6.88 (2H, s, ArH), 5.29(2H, s, CH₂ Ar), 3.82 (6H, s, OCH₃) 3.68 (3H, s, OCH₃) and 3.32 (1H,br.s, CO₂ H).

c) 6-(3,4,5-Trimethoxybenzyloxy)imidazo[1,2-b-]pyridazine-2-carboxylicacid azide

Oxalyl chloride (0.13 ml, 1.5 mmol) was added to the product of stage(b) (0.36 g, 1 mmol) and pyridine (0.079 g, 1 mmol) in dry benzene (5ml) with stirring under N₂. The mixture was heated under reflux for 3 h,cooled, and evaporated in vacuo to give a grey solid:

This solid was treated with dioxan (10 ml), water (10 ml) and sodiumazide (excess) and stirred vigorously overnight at ambient temperature.The mixture was filtered and the solid dried in vacuo to give the titlecompound as a powder (0.29 g), m.p. >139° (decomp), Nmr δH (CDCl₃) 8.35(1H, s, 3H) 7.85 (1H, J_(AB) 8.8 Hz, 8H), 6.85 (1H, J_(AB) 8.8 Hz, 7H),6.70 (2H, s, ArH), 5.31 (2H, s, CH₂ Ar), 3.90 (6H, s, OCH₃) and 3.88(3H, s, OCH₃).

d)2,2,2-Trifluoroethyl-N-[6(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b-]pyridazine-2-yl]carbamate

The product of stage (c) (2.3 g, 6 mmol), 2,2,2-trifluoroethanol (ca-3ml) and toluene (60 ml) were heated with stirring under N₂ at refluxuntil t.l.c. showed complete reaction (ca 2 h.).

The mixture was cooled overnight and filtered to give a solid which waswashed with ether and dried to give the title compound as a powder (0.43g), m.p. 205°-210° (decomp.) Nmr δ_(H) (d₆ DMSO) 10.81 (1H, br. s, NH),7.88 (1H, J_(AB) 8.8 Hz, 8H), 7.85 (1H, s, 3H), 6.90 (1H, J_(AB) 8 Hz,7H), 6.85 (2H, s, ArH), 5.25 (2H, s, CH₂ Ar) 4.83 (2H, q, J9 Hz, CH₂CF₃), 3.76 (6H, s, OCH₃) and 3.65 (3H, s, OCH₃).

EXAMPLE 242-Hydroxyethyl-N-[6(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b-pyridazin-2-yl]carbamate

A similar procedure was followed to that described in Example 23(d)except that the crude product was chromatographed on SiO₂ eluting with5% methanol-chloroform with subsequent recrystallisation from DMF-waterto yield the title compound as a powder, m.p. 193°-5°, NMR δ_(H) (d₆DMSO) 10.35 (1H, br. s, NH) 7.85 (1H, J_(AB), 8.8 Hz, 8H), 7.83 (1H, s,3H), 6.86 (1H, J_(AB) 8.8 Hz, 3H), 6.84 (2H, s, ArH), 5.25 (2H, s, CH₂Ar), 4.82 (1H, t, J4 Hz, OH), 4.15 (2H, m), 3.80 (6H, s, OCH₃) and 3.66(5H, m, OCH₂ and OCH₃).

EXAMPLE 252-(1-Morpholino)ethyl-N-[6(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin2-yl]carbamate

A similar procedure was followed to that described in Example 23(d)except that the crude product was chromatographed on SiO₂ eluting with5% methanol-chloroform and boiled with a little ethanol to give thetitle compound as a powder, m.p. 161°-162°, Nmr δH (d₆ DMSO) 10.30 (1H,br. s, NH), 7.88 (1H, s, 3H), 7.85 (1H, J_(AB), 8.8 Hz, 8H), 6.87 (1H,J_(AB), 8.8 Hz, 7H), 6.85 (2H, s, ArH), 5.26 (2H, s, CH₂ Ar), 4.22 (2H,t, J5 Hz, CO.OCH₂ 3.80 (6H, s, OCH₃), 3.68 (3H, s, OCH₃), 3.58 (4H, m,CH₂ OCH₂), 2.59 (2H, t, J5 Hz, CO.OCH₂ CH₂ N) and 2.45 (4H, m, CH₂ NCH₂).

EXAMPLE 26 MethylN-[N-Methyl-6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

Sodium hydride (1.26 g, 60%, 31.5 mMol) was added portionwise to astirred suspension of methylN-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-]pyridazin-2-yl]carbamate(9.51 g, 24.5 mMol) in DMEU (100 ml) under N₂ at ambient temperature.The mixture was treated with iodomethane (4.9 g, 2.15 ml, 35 mMol) andafter a further 1 hour the mixture was treated with molar equivalents ofsodium hydride and iodomethane. After 2 hours the mixture was pouredinto water (100 ml) and was filtered to give a white solid which waschromatographed on SiO₂ eluting with 2% methanol-chloroform. The productwas recrystallised from DMF and water to yield the title compound as awhite powder (8.29 g), m.p. 177°-178° C., NMR δH (d₆ DMSO) 8.04 (1H, s,3H), 7.96 (1H, J_(AB), 8.8 Hz, 8H), 6.92 (1H, J_(AB), 8.8 Hz, 7H), 6.86(2H, s, ArH), 5.25 (2H, s, CH₂), 3.79 (9H, s, OCH₃), 3.68 (3H, s,CO.OCH₃) and 3.42 (3H, s, NCH₃).

EXAMPLE 27 MethylN-[N-ethyl-6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]-carbamate

A similar procedure was followed as described in Example 26 to give thetitle compound as a white solid, m.p. 153°-155° C., NMR δH (d₆ DMSO),8.04 (1H, s, 3H), 7.96 (1H, J_(AB), 8.8 Hz, 8H), 6.92 (1H, J_(AB), 8.8Hz, 7H), 6.86 (2H, s, ArH), 5.25 ((2H, s, ArCH₂), 3.90 (2H, q, CH₂ CH₃),3.78 (9H, s, ArOCH₃), 3.66 (3H, s, NCH₃) and 1.19 (3H, t, CH₂ CH₃).

EXAMPLE 28 2,3-DihydroxypropylN-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

The product of Example 23(c) was reacted with solketal using a similarprocedure to that described in Example 23(d) except that upon completionof the reaction between the acyl azide and solketal the crude mixturewas evaporated in vacuo and then heated at 60°-70° C. for 0.5 hours withdilute hydrochloric acid and ethanol. The reaction mixture wasneutralised with sodium bicarbonate solution, evaporated in vacuo andchromatographed on SiO₂ eluting with 7% methanol-chloroform to give thetitle compound as a white solid, m.p. 175°-176° C., NMR δH (d₆ DMSO)10.28 (1H, brs, NH), 7.88 (1H, J_(AB) 8.8 Hz, 8H), 7.86 (1H, s, 3H),6.87 (1H, J_(AB) 8.8 Hz, 7H), 6.85 (2H, s, ArH), 5.28 (2H, s, ArCH₂),4.90 (1H, d, J4 Hz, 2'-OH), 4.65 (1H, t, J4 Hz, 1'-OH), 4.20-4.0 (2H, m,CO.OCH₂), 3.80 (6H, s, OCH₃), 3.80-3.70 (1H, m, HO-CH), 3.69 (3H, s,OCH₃) and 3.40 (2H, t, J4 Hz, HOCH₂).

EXAMPLE 29 2-DimethylaminoethylN-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]-pyridazine-2-yl]carbamate

The product of Example 23(c) was reacted with (2-dimethylamino)ethanolusing a similar procedure to that described in Example 23(d) except thatthe crude product was chromatographed on SiO₂ eluting with 5%methanol-chloroform to give a solid which was washed with ethanol anddried to give the title compound as a white powder, m.p. 185°-186° C.,NMR δH (d₆ DMSO), 10.32 (1H, brs, NH), 7.88 (1H, J_(AB), 8.8 Hz, 8H),7.85 (1H, s, 3H), 6.89 (1H, J_(AB), 8.8 Hz, 7H), 6.85 (2H, s, ArH), 5.77(2H, s, ArCH₂), 4.60 (2H, t, J4 Hz, CO.OCH₂), 3.80 (6H, s, OCH₃), 3.69(3H, s, OCH₃), 2.50 (2H, t, CH₂ N) and 2.21 (6H, s, NMe₂).

EXAMPLE 30 PhenylN-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]-carbamate

The product of Example 23(c) was reacted with phenol using a similarprocedure to that described in Example 23(d) except that the crudeproduct was chromatographed on SiO₂ eluting with 5% methanol-chloroformto give a solid which was washed with acetonitrile and dried to give thetitle compound as a white powder, m.p. 210°-213° C., NMR δH (CDCl₃)10.12 (1H, brs, NH), 8.05 (1H, s, 3H), 7.80 (1H, J_(AB), 8.8 Hz, 8H),7.55-7.15 (5H, m, Ph), 6.69 (2H, s, ArH), 6.67 (1H, J_(AB), 8.8 Hz, 7H),5.28 (2H, s, ArCH₂) and 3.90 (9H, s, OCH₃).

EXAMPLE 31 3-Amino-6-(2-bromo-3,4,5-trimethoxybenzyloxy)pyridazine

a) 3-Amino-6-(3,4,5-trimethoxybenzyloxy)pyridazine (Intermediate 1, 2.91g, 10 mMol) in acetic acid (20 ml) was created dropwise with a solutionof bromine (1.59 g, 10 mMol) in acetic acid (2 ml) over 5 minutes. After0.5 hours, the mixture was filtered to give a cream solid which wassuspended in water and basified with sodium hydroxide solution. Themixture was extracted with chloroform and the extracts were washed withwater, dried (Na₂ SO₄) and evaporated in vacuo to yield a cream solidwhich was recrystallised from toluene to give the title compound (2.76g) as cream needles, m.p. 160°-161° C., NMR δH (CDCl₃) 6.93 (1H, s, ArH)6.91 (1H, J_(AB), 8.8 Hz, 5H), 6.80 (1H, J_(AB), 8.8 Hz, 4H), 5.49 (2H,s, CH₂), 4.95 (2H, brs, NH₂), 3.91 (3H, s, OCH₃), 3.90 (3H, s, OCH₃) and3.89 (3H, s, OCH₃).

b) MethylN-[6-(2-bromo-3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

A similar procedure was followed to that described in Examples 1-3 togive the title compound as a white powder, m.p. 218°-219° C., NMR δH(CDCl₃) 9.45 (1H, brs, NH), 8.03 (1H, brs, 3H), 7.75 (1H, J_(AB), 8.8Hz, 8H), 6.94 (1H, s, ArH), 6.75 (1H, J_(AB), 8.8 Hz, 7H), 5.40 (2H, s,ArCH₂) and 3.96-3.86 (12H, m, OCH₃).

EXAMPLES 32-35

The following compounds were prepared using a similar procedure to thatdescribed in Examples 1-3:

EXAMPLE 32 MethylN-[6-(2,3-dimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

m.p. 210°-211° C., NMR δH d₆ (DMSO) 10.35 (1H, brs, NH), 7.86 (1H,J_(AB), 8.8 Hz, 8H), 7.84 (1H, s, 3H), 7.10 (3H, s, PhH), 6.88 (1H,J_(AB), 8.8 Hz, 7H), 5.35 (2H, s, CH₂), and 3.86, 3.80 and 3.72 (9H, s,OCH₃).

EXAMPLE 33 MethylN-[6-(3,5-dimethoxy-4-ethoxybenzyloxy)imidazo[1,2-b]pyridazin-2yl]-carbamate

m.p. 190°-193°, NMR δH (d₆ DMSO) 10.33 (1H, brs, NH), 7.88 (1H, J_(AB),8.8 Hz, 8H), 7.85 (1H, s, 3H), 6.88 (1H, J_(AB), 8.8 Hz, 7H), 6.85 (2H,s, ArH), 5.77 (2H, s, ArCH₂, 3.90 (2H, q, J7 Hz, CH₂ CH₃), 3.80 (6H, s,ArOCH₃), 3.69 (3H, s, CO.OCH₃) and 1.24 (3H, t, J7 Hz, CH₂ CH₃).

EXAMPLE 34 MethylN-[6-(2-t-butylbenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

m.p. 220°-223° δH (DMSO) 9.95 (1H, brs, NH), 7.85 (1H, s, 3H), 7.8 (1H,J_(AB) 8 Hz, 8H), 7.5 (2H, m, ArH), 7.28 (2H, m, ArH), 6.8 (1H, J_(AB) 8Hz, 7H), 5.5 (2H, s, CH₂), 3.7 (3H, s, OMe), 1.4 (9H, s, Me₃). (FromIntermediate 22).

EXAMPLE 35 MethylN-[6-(2-ethylbenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

m.p. 190°-191° δH (DMSO) 9.95 (1H, brs, NH), 7.85 (1H, s, 3H), 7.8 (1H,J_(AB) 8 Hz, 8H), 7.45 (1H, d, ArH), 7.3 (3H, m, ArH), 6.8 (1H, J_(AB) 8Hz, 7H) 5.4 (2H, s, O-CH₂), 3.7 (3H, s, OMe), 2.7 (2H, quad, CH₂), 1.2(3H, t, Me). (From Intermediate 23).

EXAMPLE 36 n-PropylN-[6-(2,5-dimethylbenzyloxy)imidazo[1,2-]pyridazin-2-yl]carbamate

m.p. 196°-7° δH (DMSO) 9.85 (1H, brs, NH), 7.85 (1H, s, 3H), 7.80 (1H,J_(AB) 8 Hz, 8H), 7.25 (1H, s, 6'H), 7.1 (2H, 2 d, 3'H and 4'H), 6.8(1H, J_(AB) 8 Hz, 7H), 5.35 (2H, s, OCH₂), 4.1 (2H, t, OCH₂), 2.3 (6H, 2s, 2×ArMe), 1.7 (2H, quad, CH₂), 0.95 (3H, t, Me). (Fromn-propylchloroacetylcarbamate and Intermediate 24).

EXAMPLE 37 MethylN-[6-(3,4,5-trimethylbenzyloxy)imidazo[2,1-b]pyridazin-2-yl]carbamate

m.p. 227°-229° δH (DMSO) 9.90 (1H, brs, NH), 7.85 (1H, s, 3H), 7.75 (1H,J_(AB) 8 Hz, 8H), 7.15 (2H, s, ArH), 6.80 (1H, J_(AB) 8 Hz, 7H), 5.25(2H, s, OCH₂), 3.7 (3H, s, OMe), 2.28 (6H, s, 2×ArMe), 2.15 (3H, s,ArMe). (From Intermediate 25).

EXAMPLE 38

Methyl N-[6-(2-phenylbenzyloxy)imidazo[1,2-b]pyridazin-2-yl carbamate

m.p. 203-204. δH (DMSO) 9.92 (1H, brs, NH), 7.75 (1H, J_(AB) 8 Hz, 8H),7.70 (1H, s, 3H) 7.4 (9H, m, 9 ArH), 6.75 (1H, J_(AB) 8 Hz, 7H), 5.3(2H, s, OCH₂), 3.7 (3H, s, OCH₃). (From Intermediate 26).

EXAMPLE 39 MethylN-[6-(3-diethylaminobenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamatehydrochloride

m.p. 220°-225° δH(DMSO), 10.35 (1H, brs, NH), 7.9 (1H, J_(AB) 8 Hz, 8H),7.8 (1H, s, 3H), 7.6 (4H, m, 4×ArH), 6.9 (1H, J_(AB) 8 Hz, 7H), 5.4 (2H,s, CH₂ O), 3.7 (3H, s, OMe) 3.5 (4H, brs, 2×CH₂ N), 1.05 (6H, t, 2×Me).(From Intermediate 27).

EXAMPLE 40 MethylN-[6-(3-methylaminobenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamatehydrochloride

m.p. 213°-215° (dec) δH(DMSO) 10.4 (1H, brs, NH), 7.9 (1H, J_(AB) 8 Hz,8H), 7.85 (1H, s, 3H), 7.3 (4H, m, 4 ArH), 6.9 (1H, J_(AB) 8 Hz, 7H),5.4 (2H, s, CH₂ O), 3.7 (3H, s, OMe), 2.85 (3H, s, MeN). (FromIntermediate 28).

EXAMPLE 41 EthylN-[6-(3-dimethylaminobenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

m.p. 204-8 δH(DMSO) 9.95 (1H, brs, NH), 7.85 (1H, s, 3H), 7.80 (1H,J_(AB) 8 Hz, 8H), 7.2 (1H, t, 5'H), 6.85 (1H, J_(AB) 8 Hz, 7H), 6.75(3H, m, 3 ArH), 5.3 (2H, s, CH₂ O), 4.2 (2H, quad, OCH₂), 2.9 (6H, s,Me₂ N), 1.25 (3H, t, Me). (From Intermediate 7).

EXAMPLE 42 EthylN-[6-(1-naphthylmethoxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

m.p. 240°-245° δH(DMSO), 10.0 (1H, brs, NH), 8.2 (1H, m, ArH), 8.05 (2H,m, 2 ArH), 7.95 (1H, s, 3H), 7.90 (1H, J_(AB) 8 Hz, 8H), 7.85 (1H, d,2'H), 7.65 (3H, m, 3 ArH), 6.90 (1H, J_(AB) 8 Hz, 7H), 5.95 (2H, s, CH₂O), 4.25 (2H, quad, OCH₂), 1.35 (3H, t, Me). (From Intermediate 3)

EXAMPLE 43 n-PropylN-[6-(1-naphthylmethoxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

m.p. 208°-210° δH(DMSO), 10.25 (1H, brs, NH), 8.15 (1H, m, ArH), 8.00(2H, m, 2 ArH), 7.90 (1H, s, 3H), 7.85 (1H, J_(AB) 8 Hz, 8H), 7.75 (1H,d, 2'H), 7.60 (3H, m, 3 ArH), 6.85 (1H, J_(AB) 8 Hz, 7H), 5.8 (2H, s,OCH₂), 4.1 (2H, t, OCH₂), 1.65 (2H, m, CH₂), 0.9 (3H, t, Me). (FromIntermediate 3).

EXAMPLE 44 MethylN-[6-(3-methoxy-1-naphthylmethoxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

δH (DMSO) 10.0 (1H, brs, NH), 8.1 (1H, d, ArH), 7.9 (2H, m, ArH+3H),7.85 (1H, J_(AB) 8 Hz, 8H), 6.85 (1H, J_(AB) 8 Hz, 7H), 5.8 (2H, s, CH₂O), 3.90 (3H, s, OMe), 3.7 (3H, s, OMe). (From Intermediate 29 ).

EXAMPLE 45 MethylN-[6-[2-[3,4,5trimethoxyphenyl)ethoxy]imidazo[1,2-b]pyridazin-2-yl]carbamate

m.p. 203°-6° δH (DMSO) 9.95 (1H, brs, NH), 7.80 (1H, s, 3H), 7.75 (1H,J_(AB) 8 Hz, 8H), 6.8 (1H, J_(AB) 8 Hz, 7H), 6.65 (2H, s, 2 ArH), 4.5(2H, t, CH₂ O), 3.8 (6H, s, 3 MeO, 5 MeO ), 3.7 (3H, s, OMe), 3.65 (3H,s, 4 MeO), 3.0 (2H, t, CH₂). (From Intermediate 30).

EXAMPLE 46 MethylN-6-(3,4,5-trimethoxyphenethyl)imidazo[1,2-b]pyridazin-2-ylcarbamate a)4-Oxo-6-(3,4,5-trimethoxyphenethyl)hex-5-enoic acid

A solution of laevulinic acid (50 g, 0.43 mol) in water (200 ml) wasadded to a mixture of 3,4,5-trimethoxybenzaldehyde (85 g, 0.43 mol) inethanol (150 ml) and sodium hydroxide solution (5%, 700 ml). The mixturewas warmed with vigorous stirring until all the aldehyde had dissolvedand was then poured onto ice (ca 2 Kg). It was then acidified to pH3-4and left overnight. The crystalline material formed was filtered off,dried in vacuo and then recrystallised from ethanol to give pale yellowcrystals (30.08 g), m.p. 187°-9°.

N.m.r. δH (d₆ -DMSO), 7.57 (1H, d, J_(A1B1) =18.0 Hz, CH), 7.08 (2H, s,2'H, 6'H), 6.91 (1H, d, J_(AB) =18.0 Hz, CH), 3.83 (6H, s, 3'-MeO and5'MeO), 3.70 (1H, s, 4'MeO), 3.33 (1H, br. m. unres, CO₂ H), 2.92 (2H,t, J_(A2B2) =7.0 Hz, CH₂) and 2.50 2H, t, J_(A2B2) =7.0 Hz, CH₂).

b) 4,5-dihydro-6-(3,4,5-trimethoxy-α-styryl)pyridazin-3(2H)-one

4-Oxo-6-(3,4,5-trimethoxyphenethyl)hex-5-enoic acid (20 g, 0.068 mol)was dissolved in glacial acetic acid (240 ml) and then hydrazine hydrate(3.4 g, 0.068 mol) was added. The mixture was heated under reflux for2.5 h, cooled and poured into water (ca 21). After standing overnight,the crystals formed were filtered at the pump and dried in vacuo to givethe product (13.58 g). A portion (3.5 g) was recrystallised frommethanol and gave pale yellow crystals (3.18 g), m.p. 173°-5°.

N.m.r. δH (CDCl₃), 8.91 (1H, brs, NH), 6.82 (2H, s, CH, CH), 6.70 (2H,s, CH, CH), 3.89 (6H, s, 3'-MeO and 5'-MeO), 3.87 (3H, s, 4'-MeO), 2.82(2H, t, J_(AB) =9.0 Hz) and 2.56 (2H, t, J_(AB) =9.0 Hz).

c) 4,5-Dihydro-6-(3,4,5-trimethoxyphenethyl)pyridazin-3-(2H)-one

4,5-Dihydro-6-(3,4,5-trimethoxy-α-styryl)pyridazin-3(2H)-one (5g, 0.017mol) was hydrogenated (85°, 10 atm H₂) on glacial acetic acid (150 ml)in the presence of 10% Pd/C catalyst (0.25 g until the requisite uptakeof hydrogen had occurred. The mixture was then filtered through Hyflo,and the filtrate evaporated in vacuo at 35°. The remaining traces ofglacial acetic acid were removed by azeotroping with toluene and thebrown solid (4.9 g) purified further by silica gel chromatography, with1% methanol/dichloromethane as the eluent. Removal of the solvent fromthe appropriate fractions gave the product as a white solid (3.04 g),m.p. 116°-117°.

N.m.r. δH (CHCl₃), 8.46 (1H, s, br, NH), 6.43 (2H, s, 2'H, 6'H), 3.83(6H, s, 3'MeO and 5'MeO), 3.81 (3H, s, 4'MeO), 2.84 (2H, t, J_(AB) =7Hz, CH₂), 2.61 (2H, t, J_(AB) =7 Hz) and 1.95 (4H, m, part. res, CH₂,CH₂).

d) 6-(3,4,5-Trimethoxyphenethyl)pyridazin-3(2H)-one

4,5-Dihydro-6-(3,4,5-trimethoxyphenethyl pyridizan-3(2H)-one (1.72 g,5.93 m mol) and selenium dioxide (0.98 g, 8.83 m mol) was refluxed inethanol (80 ml) for 4.5 days. More selenium dioxide (0.5 g, 4.51 m mol)was added and the mixture was refluxed for a further 5 days. The mixturewas filtered to remove selenium which had separated and the filtrateevaporated in vacuo to give a brown sticky solid (2.21 g). This solidwas subjected to flash chromatography on silica with 1-2%methanol-dichloromethane as the eluent. Combination of the appropriatefractions gave the product as a sandy-brown crystalline solid (1.43 g),m.p. 122-4°.

N.m.r. δH (CDCl₃) 11.64 (1H, brs, NH), 7.08 (1H, d, J_(AB) =6Hz, HetCH),6.89 (1H, d, J_(AB) =6Hz, HetCH), 6.48 (2, s, 2'H), 3.83 (9H, 2 s, 3'MeOand 5'MeO 4'MeO) and 2.82 (4H, s, CH₂ --CH₂).

e) 3-Chloro-6-(3,4,5-trimethoxyphenethyl)pyridazine

A mixture of 6-(3,4,5-Trimethoxyphenethyl)pyridazin-3(2H)-one (2.80 g;9.65 mmol) and phosphorus oxychloride (70 ml) was heated at 100° for 1h, cooled to room temperature and hydrolysed by careful, gradualaddition to water over 3 h, so that the temperature did not exceed 30°.The mixture was then basified to pH12 by the addition of sodiumhydroxide solution (10N, 700 ml) and then left at 4° overnight. Theprecipitate was filtered at the pump, washed well with water to removeinorganic salts and the residue on the sinter taken up indichloromethane. After drying (sodium sulphate), removal of the solventgave a light-brown solid (2.84 g) which was purified by `flash`chromatography on silica, with 10% of ethyl acetate/dichloromethane asthe eluent. Appropriate fractions were combined to give a white solid(2.16 g), m.p. 105°-106°.

N.m.r. δH (CDCl₃) 7.38 (1H, d, J_(AB) =9 Hz, HetCH), 7.16 (1H, d, J_(AB)=9 Hz, HetCH), 6.37 (2H, s, 2'H, 6'H), 3.82 (9H, s, 3'MeO, 4'MeO and5'MeO), 3.37 (2H, t, J_(A2B2) =9H, CH₂), and 3.04 (2H, t, J_(A2B2), 9HzCH₂).

f) 3-Amino-6-(3,4,5-trimethoxyphenethyl)pyridazine

3-Chloro-6-(3,4,5-trimethoxyphenethyl)pyridazine (1.97 g, 6.38 mol) inmethanolic ammonia (saturated, 800 ml) was heated in a stainless steelautoclave at 150° for 65 h and then allowed to cool. The mixture wasthen evaporated, in vacuo to give a dark-brown sticky solid (2.84 g),which was subjected to flash chromatography on silica with 3%methanol/dichloromethane as the eluent. Combination of the relevantfractions afforded the product as a white solid (0.56 g), m.p.130°-132°.

N.m.r. δH (CDCl₃) 6.96 (1H, d, J_(AB) =9.0 Hz, HetCH), 6.67 (1H, br, d,J_(AB) =9.0 Hz, HetCH), 6.42 (2H, s, 2'H 6'H), 4.74 and 1.98 (2H, brs,-NH₂), 3.83 (9H, s, 3'MeO, 4'MeO 5'Meo), 3.13 (2H, part res m., CH₂) and3.01 (2H part res. m., CH₂).

g) Methyl N-6-(3,4,5-trimethoxyphenethyl)imidazo[1,2-b-]pyridazin-2-ylcarbamate

3-Amino-6-(3,4,5-trimethoxyphenethyl) pyridazine (0.50 g, 1.73 mmol) andmethyl N-chloroacetylcarbamate (0.26 g; 1.74 mmol) were heated in dryhexamethylphosphoramide (distilled from CaH₂ in vacuo, 15 ml) withstirring for 4 h at 100° C. under nitrogen. The mixture was then cooled,poured into water (150 ml), whereupon a precipitate formed. Afterstanding overnight the precipitate was filtered off and dried in vacuoto yield a cream-coloured crystalline solid (0.53 g). This was purifiedfurther by flash chromatography (silica, 1-2% methanol/dichloromethaneas eluent) and crystallisation from ethyl acetate to give off-whitecrystals (0.18 g), m.p. 175°-6°.

N.M.R. δH (CDCl₃) 10.17 (1H, br.s, NH), 8.18 (1H, br.s, Het 3-H); 7.77(1H, d, JAB=10 Hz, Het CH), 6.85 (1H, d, JAB=10 Hz, HetCH), 6.42 (2H, s,2'-H, 6'-H), 3.88 (3H, s, CO₂ Me) and 3.82 (9H, s, 3-MeO, 4'-MeO,5'-MeO) , 3.12 (2H, part.res.m, CH₂) and 3.02 (2H, part.res.m, CH₂).

EXAMPLE 47 MethylN-6-(3,4,5-trimethoxy-α-styryl)imidazo[1,2-b]pyridazin-2-ylcarbamate a)6-(3,4,5-trimethoxy-α-styryl)pyridazin-3(2H)-one

The compound of Example 46(b) (10.0 g, 34.4 mmol) and selenium dioxide(10 g, 90.1 mmol) were heated under reflux in ethanol (300 ml) for 80 h.A further charge of selenium dioxide (10 g) was added and the refluxcontinued for a further 40 h. The reaction mixture was then filteredthrough `Hyflo`, evaporated and the residue dried in vacuo to give adark-brown sticky solid (14.48 g). This was then chromatographed onsilica with 1-2% methanol/dichloromethane. Combination of theappropriate fractions, followed by crystallisation from methanolafforded the product as a sandy-brown solid (5.57 g), m.p. 194°-196° C.

N.M.R. δh (CDCl₃) 11.95 (1H, br, s, NH) 7.66 (1H, d,J_(A).sbsb.1.spsb.B.sbsb.1 =10 Hz, Het CH), 7.10 (1H, d,J_(A).sbsb.2.spsb.B.sbsb.2 =18 Hz, CH), 7.01 (1H, d, J_(A)_(A).sbsb.1.spsb.B.sbsb.1 =10 Hz, HetCH), 6.92 (1H, d,J_(A).sbsb.2.spsb.B.sbsb.2 =18 Hz, CH), 6.74 (2H, s, 2'-H), 3.91 (6H, s,3'-MeO, 5'-MeO) and 3.88 (3H, 4'-MeO).

3-Chloro-6-(3,4,5-trimethoxy-α-styryl)pyridazine

6-(3,4,5-trimethoxy-α-styryl)pyridazin-3(2H)-one (5.3 g, 0.018 mol) inphosphorus oxychloride (150 ml) was heated at 100° for 1.25 h. Themixture was then added to water (31) over 2 h, keeping the temperaturein the range 10°-30° C. The mixture was then carefully basifed to pH10with sodium hydroxide solution (10N, 1.31). After standing overnight,the precipitate was filtered off and dried in vacuo to give the productas a sand-brown solid (6.24 g). A portion recrystallised from ethanolhad m.p. 162°-163.5° C.

N.m.r. δh (CDCl₃) 7.64 (1H, d, J_(A).sbsb.1.spsb.B.sbsb.1 =10 Hz, HetCH), 7.54 (1H, d, J_(A).sbsb.2.spsb.B.sbsb.2 =18 Hz, CH), 7.48 (1H, d,J_(A).sbsb.1.spsb.B.sbsb.1 =10 Hz, Het CH), 7.27 (1H, d,J_(A).sbsb.2.spsb.B.sbsb.2 =18 Hz, CH), 6.82 (2H, s, 2'-H, 6'-H, 3.92(6H, s, 3'-MeO and 5'-MeO) and 3.88 (3H, s, 4'-Meo).

(c) 3-Amino-6-(trimethoxy-α-styryl)pyridazine

3-Chloro-6-(3,4,5-trimethoxy-α-styryl)pyridazine(5.5 g, 17.1 mmol) inmethanolic ammonia (saturated, 800 ml) was heated in a stainless steelautoclave at 150° C. for 100 h and then allowed to cool. Removal of thesolvent and chromatography on silica (2methanol/dichloromethane)afforded the product as a light-brown solid (1.58 g), m.p. 139°-142°

N.m.r. δh (CDCl₃) 7.49 (1H, d, J_(A).sbsb.1.spsb.B.sbsb.1 =10 Hz CH),7.24 (2H, 2×superimposed d, J_(A).sbsb.1.spsb.B.sbsb.1,J_(A).sbsb.2.spsb.B.sbsb.2 =(10 Hz, 2×CH), 6.75 (3H, d, superimposed ons, J_(A).sbsb.2.spsb.B.sbsb.2 =10 Hz, CH, 2'-H, 6'-H)-4.85 (2H, br. s,NH₂), 3.92 (6H, s, 3-MeO and 5-MeO) and 3.87 (3H, s, 4-MeO).

(d) Methyl N-6-(3,4,5-trimethoxy-α-styryl)imdazo[1,2-b]pyridazin-2-ylcarbamate

3-Amino-6-(3,4,5-trimethoxy-α-styryl)pyridazine (1.36 g, 4.72 mmol) andmethyl N-chloroacetylacarbamate (0.68 g, 4.49 mol) were heated in dryhexamethylphosphoramide (distilled from CaH₂ in vacuo 30 ml) withstirring for 4 h at 100°. The mixture was then cooled and poured intowater (40 ml). The precipitate which formed was filtered off and driedin vacuo to give a yellow-brown solid (1.0 g). This was chromatographedon silica to give the product as a pale yellow solid (0.4 g), m.p.217°-9°.

N.m.r. δH (d₆ -DMSO) 10.49 (1H, br, s, NH), 7.99 (1H, s, Het 3-H), 7.94(2H, d, JA₁ B₁ 10 Hz, HetCH), 7.60 (2H, d, JA₂ B₂ =18 Hz, CH), 7.58 (2H,d, JA₁ B₁ =10 Hz, HetCH), 7.28 (2H, d, JA₁ B₂ =18 Hz, CH), 7.04 (2H, s,2'H, 6'H), 3.87 (6H, s, 3'-MeO and 5'-MeO), [3.72 (3H, s) and 3.70 (2H,s)] (CO₂ Me and 4'-MeO).

EXAMPLE 48 MethylN-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

6-(3,4,5-Trimethoxybenzyloxy)imidazo[1,2-b]pyridazine-2-carboxylic acidazide (Example 23C) (1.0 g, 2.6 mmol) was heated under reflux for 24 hin toluene (20 ml) and methanol (ca 1.5 ml). The mixture was cooled andevaporated in vacuo to give a yellow solid which was recrystallised fromDMF and water to yield the title product (1.05 g), mp. 213°-215° C. andNMR identical to the product of Example 1.

EXAMPLE 49 MethylN-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2yl]carbamate a)2-Amino-6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazinetrifluoroacetate.

t-ButylN-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate(Example 13, 0.43 g, 1 mmol) was dissolved in dichloromethane (2 ml) andtreated with trifluoroacetic acid (1 ml). After 2 h at ambienttemperature the mixture was evaporated in vacuo to give a brown oilwhich was triturated with diethyl ether to give the title compound (0.25g) as a cream solid, m.p. 150°-157°, NMR δ_(H) (DMSO) 8.0 (1H, J_(AB)8.8 Hz, 8H), 7.48 (1H, s, 3H), 7.16 (1H, J_(AB) 8.8 Hz, 7H), 6.44 (2H,s, CH₂), 4.5 (brs, NH₃), 3.89 (6H, s, OMe) and 3.75 (3H, s, OMe).

b) MethylN-6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazine-2-yl]carbamate

The product of stage (a) (1.0 g, 3.03 mmol) was suspended indichloromethane and shaken with dilute sodium hydroxide solution. Theorganic phase was dried (Na₂ SO₄) and evaporated to give a brown oilwhich was dissolved in dichloromethane and treated, with stirring, withtriethylamine (0.42 ml, 3.03 mmol), methyl chloroformate (0.23 ml, 3.03mmol) and 4-dimethylaminopyridine (18 mg, 0.3 mmol). The mixture wasstirred at ambient temperature for 17 h then heated under reflux for 2 hand evaporated in vacuo. The resulting solid was partioned betweenchloroform and water, the organic phase was separated, dried (Na₂ SO₄)and evaporated to give a solid which was chromatographed on SiO₂ elutingwith 2% methanol-chloroform. The product was recrystallised from DMF-H₂O to give the title compound (0.27 g), mp. 210°-212°, NMR identical tothe product of Example 1.

EXAMPLES 50-52

The following compounds were prepared using a similar procedure to thatdescribed in Examples 1-3:

EXAMPLE 50 MethylN-[6-(2,5-Dimethylbenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

mp. 208°-209° Nmr δH (d₆ -DMSO), 10.05 (1H, br.s, NH), 7.95 (1H, J_(AB)8.8 Hz, 8H), 7.85 (1H, s, 3-H), 7.35 (1H, s, 6'-H), 7.20 (2H, J_(AB) 8.8Hz, 7H+d, 3' or 4'-H), 6.90 (1H, d, 3' or 4'-H), 5.90 (2H, s, CH₂), 3.80(3H, s, OMe), 2.4 (3H, s, Me), 2.35 (3H, s, Me).

EXAMPLE 51 MethylN-[6-(2-pyridylmethoxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

mp. 231°-233° (dec) Nmr δH (d₆ -DMSO), 9.95 (1H, br.s, NH), 8.55 (1H, d,6'-H), 7.85 (3H, m, 8-H+3-H+5'-H), 7.55 (1H, d, 3'-H), 7.35 (1H, m,4'-H), 6.90 (1H, J_(AB) 8.8H_(z), 7-H), 5.45 (2H, s, CH₂), 3.70 (3H, s,OMe). (From Intermediate 31).

EXAMPLE 52 MethylN-[6-(2-furfuryloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

mp. 220°-224° Nmr δ_(H) (d₆ -DMSO), 10.05 (1H, br.s, NH), 7.95 (1H, s,3-H), 7.90 (1H, J_(AB) 8.8H_(z), 8-H), 7.75 (1H, brs, 5'-H), 6.90 (1H,J_(AB) 8.8H_(z), 7-H), 6.75 (1H, d, 4'-H), 6.55 (1H, br.s, 3'-H), 5.45(2H, s, CH₂), 3.80 (3H, s, OMe). (From Intermediate 32).

BIOLOGICAL TEST RESULTS A) Tubulin Polymerisation Assay Materials andMethods 1. Preparation of tubulin

a) Fresh horse brain

b) Buffers:

    ______________________________________                                        BBG     BB          BB2G                                                      ______________________________________                                        100  mM     MES*/NaOH   As BBG but                                                                              As BBG but                                  2    mM     EGTA*       without   with 8 M glycerol                           1    mM     MgSO.sub.4  glycerol  and 1 mM GTP*                               4    M      glycerol                                                          2    mM     dithioerythritol                                                  pH 6.9 at 23° C.                                                       ______________________________________                                         *MES = 2(Nmorpholino) ethane sulphonic acid                                   EGTA = ethylene glycol bis (aminoethyl ether)N,N,N',Ntetraacetic acid         GTP = guanosine triphosphate                                             

All manipulations are performed at 4° C. unless otherwise specified. Thehorse brain is washed in ice-cold BBG buffer and superficial meningesand blood vessels removed. After weighing, cerebral cortices arechopped, homogenised in 75 ml BBG buffer/100 g brain, centrifuged at6500 g for 15 min and after removal of supernatant, re-centrifuged at100,000 g for 75 min. The volume of the supernatant (Vml) is measuredand V/10 ml 10 mM GTP (Li salt) in H₂ O added. The mixture is incubatedin sealed centrifuge tubes (30 min, 34° C.) in a shaking water bath topolymerise the tubulin. After polymerisation the tubes are balanced andcentrifuged at 100,000 g, (1 h at 27° C.) in a pre-warmed rotor. Thehigh-speed pellet is resuspended in V/4 ml BB buffer and the preparationstirred on ice for 30 min and centrifuged at 100,000 g (1 h at 4° C.) toremove the cold-stable microtubules. An equal volume of BB2G buffer isadded to the supernatant which is frozen rapidly in 5 ml samples inplastic weighing dishes floated on a solid CO₂ /ethanol slurry, andstored overnight at -80° C. Afer ca. 18 hours the frozen samples oftubulin are thawed, 10 mM GTP in H₂ O added to give a finalconcentration of 1 mM, and the new volume (Wml), is measured. Thepolymerisation/depolymerisation cycle is repeated exactly as above butsubstituting W for V to give twice-cycled tubulin.

2. Turbidimetric assay of tubulin polymerisation

Apparatus: recording spectrophotometer with a 6-position, thermostattedcuvette holder; full scale deflection=0.2 absorbance units.

In a 1 ml spectrophotometer cuvette are mixed 100 μl 10 μmM GTP (Lisalt) made up in BB buffer, 10 μl H₂ O or DMSO - depending on selecteddrug solvent, BB buffer and tubulin preparation such that the finalincrease in A₃₅₀ nm is 0.15 units after 16 mins (approx. 100 μl oftubulin prep. or 2.5 mg protein) in a final volume of 1 ml at 37° C. Allreagents are stored on ice.

Polymerisation is initiated by raising the temperature to 37° C. and theincrease in A₃₅₀ nm of triplicate samples against a reference cuvette isrecorded. The reference sample includes a similar incubation mixtureeither without tubulin or with the addition of 1 mM Ca²⁺. The increaseover initial A₃₅₀ nm 10 min after the completion of lag phase (controlpolymerisation is 80% complete within this time) is calculated andexpressed as a percentage of the control value, for a range of drugconcentrations. The drug concentration required to give a 50% change(IC₅₀) in the control value is determined.

Results

                  TABLE 1                                                         ______________________________________                                        Compound of Total tubulin polymerisation                                      Ex. No      IC.sub.50 (μm)                                                 ______________________________________                                        1           0.42                                                              2           0.14                                                              3           0.41                                                              4           0.37                                                              5           0.49                                                              7           0.52                                                              8           0.23                                                              9           0.89                                                              11          4.24                                                              12          1.21                                                              ______________________________________                                    

B) P338D₁ Colony-forming Assay Method

In this assay, cells from an in vitro-adapted line of the mouse lymphoidneoplasm, P388 are first exposed to serially diluted concentrations oftest compound over a 24 hour period in culture. Thereafter, the abilityof such treated cells to form discrete colonies over a 14 day periodafter resuspension in a semi-solid drug-free medium is determined.

Initially cells in log growth are plated into individual 25 cm² tissueculture flasks each containing a final volume of 5 mls of Hepes bufferedRPMI 1640 culture medium supplemented with 10 percent foetal calf serum,antibiotics and test compound. All compounds are formulated initially atappropriate concentrations in DMSO, 25 microliters of which is thenadded to each flask. All compounds are evaluated at concentrationsranging serially in four fold decrements from a top concentration somefour fold greater than that already known to inhibit the proliferationof these cells by about 80 to 90 percent in the primary proliferativeassay.

After 24 hrs exposure to the test compound the cells are counted and aknown number of live cells transferred to a 15 ml centrifuge tube towhich 4 mls of a 0.25 percent low temperature gelling agarose solutionin complete RPMI tissue culture medium is then added. After 13 daysincubation at 37° C., 1 ml of 1% p-Iodonitrotatrazolium violet is addedto the top of each tube and allowed to permeate through the agarose fora further 24 to 48 hrs. This dye is metabolised by living cells toproduce an insoluble red crystalline product which facilitates countingof the colonies. Samples are taken from each tube and the number ofcolonies containing a minimum of 50 cells is determined. Theconcentration of compound necessary to inhibit colony formation by 50percent relative to that of control cells incubated under identicalconditions but in the absence of the test compound is determined.

Results

                  TABLE 2                                                         ______________________________________                                        P388 D.sub.1 Colony-forming Assay                                             Compound of Example No.                                                                          IC.sub.50 (M)                                              ______________________________________                                        1                  1.32 × 10.sup.-8                                     2                  .sup. 5.16 × 10.sup.-10                              3                  2.15 × 10.sup.-9                                     4                  5.12 × 10.sup.-9                                     5                  1.26 × 10.sup.-8                                     7                  6.34 × 10.sup.-9                                     8                  2.93 × 10.sup.-9                                     11                 4.10 × 10.sup.-8                                     ______________________________________                                    

C. Lymphocytic Leukemia P388/O Test Method

CD2-F₁ mice, of the same sex, weighing within a 3 gram range surrounding20 g, are used for this test. Control and test animals are injectedintraperitoneally with a suspension of 10⁶ viable P388/O tumour cells onday 0. In each test several dose levels which bracket the LD₂₀ for thecompound are evaluated; each dose level group contains 6 animals. Thetest compounds are prepared either in physiologic saline containing0.05% Tween 80 or distilled water containing 5% dextrose and areadministered intraperitoneally on days 1,5 and 9 relative to tumourimplant. Doses are on a mg/kg basis according to individual animals'body weights. The day of death for each animal is recorded and themedian day of death identified for each group. The difference betweenthe median survival time for treated and control groups is expressed asa percentage increase in life span (% ILS).

Results

                  TABLE 3                                                         ______________________________________                                        Lymphocytic Leukemia P388/0 Test                                              Compound of Dose     %       30 Day 60 Day                                    Example No. (mg/kg)  ILS     survivors                                                                            survivors                                 ______________________________________                                        1            10      300     6/6    2/6                                       2              7.3    31                                                      3            50      136                                                      4            20       44                                                      5           150       61                                                      7            5       111                                                      8            10       44                                                      9           200      180                                                      11          675      155     1/6    0/6                                       12          675      170                                                      26          300      263                                                      32          750      280            1/6                                       33          200      240            3/6                                                                           (Day 51)                                  ______________________________________                                    

D. LD₂₀ (Mouse) Method

Test compounds are prepared as described for the lymphocytic leukemiaP388/O test (C) and administered intraperitoneally at various doselevels to groups of 6 CD2-F₁ mice, of the same sex, weighing 20±3 g, ondays 1, 5 and 9. The mice are observed for up to 14 days (from day 1),the number of deaths in each group recorded and the LD₂₀ determined.

Results

                  TABLE 4                                                         ______________________________________                                        Compound of    ID.sub.20                                                      Example No     (mg/kg)                                                        ______________________________________                                        1              20-30                                                          2               5                                                             3              200                                                            4               20                                                            5              140                                                            7               15                                                            8               15                                                            9              450                                                            11             >450                                                           12             >450                                                           26             450                                                            31             165                                                            32             >450                                                           ______________________________________                                    

E. Activity Against Drug-Resistant Tumors

Using a similar procedure to the Lymphocytic Leukaemia P388/O test, thecompound of Example 1 was evaluated against P388/O tumours which hadbeen made resistant to the following standard, clinically usedanti-tumour agents:

bis-chloronitrosourea (BCNU)

cylophosphamide (CPA)

adriamycin (ADR)

actinomycin D (ActD)

methotrexate (MTX)

5-fluorouracil (5 FU)

Cis-platinum (Cis-Pt)

Vincristine (VCR)

Amsacrine (AMSA)

Results

                  TABLE 5                                                         ______________________________________                                        In vivo activity of the                                                       Compound of Example 1 against drug resistant tumours                          Tumour/            Optimum     %     60 Day                                   Resistance                                                                             Compound  Dose (mg/kg)                                                                              ILS   Survivors                                ______________________________________                                        P388/BCNU                                                                              Ex. 1     7.5         +131  0/6                                               BCNU      2.0         +36   0/6                                      P388/Cis-Pt                                                                            Ex. 1     10.0        +50   1/6                                               Cis-Pt    5.3         +21   0/6                                      P388/AMSA                                                                              Ex. 1     5.0         +134  4/6                                                                           (day 31)                                 P388/ADR Ex. 1     10.0        +90   0/6                                               ADR       4.5         +27   0/6                                      P388/MTX Ex. 1     7.5         +100  1/6                                               MTX       3.0         +15   0/6                                      P388/ActD                                                                              Ex.1      12.5        +109  1/6                                               ActD      0.5         +27   0/6                                      P388/CPA Ex. 1     12.5        +150  1/6                                               CPA       265.0       +55   0/6                                      P388/VCR Ex. 1     12.5        +145  3/6                                               VCR       1.5         +36   0/6                                      P388/5FU Ex. 1     10.0        +92   0/6                                               5FU       20.0        +71   0/6                                      ______________________________________                                    

F. In Vito Activity against Human Tumour Cell Lines Method

Cells from the human tumour cell lines DLD-1, HCT-116, WiDr and A549 areexposed to serially diluted concentrations of test compounds over a 96hour period in culture. The ability of such cells to proliferate overthe test period is determined.

Cells in log growth are plated into 96 well multiwell tissue culturedishes in 100 μl/well of RPMI 1640 culture medium supplemented with 10%foetal calf serum, antibiotics and test compound. All compounds areformulated initially at appropriate concentrations in DMSO, the finalconcentrations in this solvent being twenty times that required in theplate. A final 1 in 10 dilution in complete medium is then made beforeadding 100 μl to each well of the plate. All compounds are evaluated atconcentrations ranging serially in four fold decrements from a topconcentration some four fold greater than that already known to inhibitthe proliferation of cells from the mouse lymphoid neoplasm, P388D1 byabout 80 to 90 percent in a primary proliferative assay.

After 96 hours the proliferation of cells exposed to test compound iscompared with control untreated cells by one of two methods:

a) Culture supernatants are aspirated and cells fixed and stained byadding a solution of methylene blue (5 g per liter of 50% ethanol:water, 100 μl/well). After 30 minutes at room temperature unbound stainis washed off by immersing plates in water. Stained cells aresolubilised overnight using 1% Sarkosyl (Sigma) in phosphate-bufferedsaline (100 μl/well). Absorbances are read by an ELISA platespectrophotometer at a wavelength of 620 nm. The IC50 is defined as thatconcentration of drug which decreases absorbance to 50% of that incontrol (drug-free) cultures. This method is used for the DLD-1 cellline.

b) 20 μl of MTT (5 mg/ml in PBS) is added to each well. After anincubation period of 4 hours the medium from each well is aspirated andreplaced with 200 μl DMSO to dissolve the formazan crystals formed.Absorbances are read by an ELISA plate spectrophotometer at a wavelengthof 540 nm. The IC50 is defined as that concentration of drug whichdecreases absorbance to 50% of that in control (drug-free) cultures.This method is used for the WiDr, HCT-116 and A549 cell lines.

                  TABLE 6                                                         ______________________________________                                        In Vitro Activity against human tumour cell lines                             Compound of                                                                             IC.sub.50 (μM) × 10.sup.-3                                 Example No                                                                              DLD-1.sup.(a)                                                                          WiDr.sup.(b)                                                                             HCT-116.sup.(b)                                                                       A549.sup.(b)                            ______________________________________                                        1         11.60    30.00      9.20    23.97                                   2         2.90     4.57       2.80    3.42                                    3         1.35     0.92       1.91    1.92                                    4         6.63     10.98      5.45    20.81                                   5         7.34     3.65       3.30    4.36                                    7         5.92     19.70      8.25    22.40                                   8         8.82     41.00      20.52   38.96                                   ______________________________________                                    

G. In vivo activity of the compound of Example 1 against murine tumours

Using a similar procedure to the Lymphocytic Leukaemia P388/O test thecompound of Example 1 was evaluated against the murine tumours B16,L1210 and M5076. A suspension of 10⁶ tumour cells is implantedintraperitoneally into control and test animals on day zero. B16 tumourcells are administered intraperitoneally as a 1:10 Brei of cells on dayzero. The test compound is administered intraperitoneally on days 1, 5and 9. For the B16 and M5076 tests there are 10 mice per treated groupand for L1210 there are 6 mice per treated group. The day of death foreach animal is recorded and the % ILS (percentage increase in life-span)calculated. The results are given in Table 7.

                  TABLE 7                                                         ______________________________________                                        In Vivo Activity against murine tumours                                                Dose         Mean % ILS No of                                        Tumour   (mg/kg)      (±SEM)  expts                                        ______________________________________                                        M5076    5            28           1                                          L1210    10           134    (±72)                                                                            2                                          B16      5            69     (±4)                                                                             3                                          ______________________________________                                    

FORMULATION EXAMPLES A. Tablet

    ______________________________________                                        Compound of Formula I (as hydrochloride)                                                                100.0 mg                                            Pregelatinised Corn Starch                                                                              60.0 mg                                             Sodium Starch Glycollate  20.0 mg                                             Magnesium Stearate        4.0 mg                                              ______________________________________                                    

The Compound of formula (I) is finely ground and intimately mixed withthe powdered excipients, pregelatinised corn starch and sodium starchglycollate. The powders are wetted with purified water to form granules.The granules are dried and mixed with the magnesium stearate. Theformulation is then compressed into tablets weighing approximately 184mg each.

B. Tablet

    ______________________________________                                        Compound of formula (I) 100.0 mg                                              Sodium Starch Glycollate                                                                              20.0 mg                                               Lactose                 83.8 mg                                               Magnesium Stearate      4.2 mg                                                Polyvinylpyrrolidone    14.0 mg                                               ______________________________________                                    

The Compound of formula (I) is finely ground and intimately mixed withthe powdered excipients, sodium starch glycollate and lactose. Thepowders are wetted with a solution of polyvinylpyrrolidone dissolved inpurified water and denatured alcohol to form granules. The granules aredried and mixed with the magnesium stearate. The formulation is thencompressed into tablets weighing approximately 222 mg each.

C. Capsules

    ______________________________________                                        Compound of formula (I) 100.0 mg                                              Corn Starch             50.0 mg                                               Magnesium Stearate      3.0 mg                                                ______________________________________                                    

The finely divided compound of formula (I) is mixed with powdered cornstarch. The dried powder is mixed with magnesium stearate and filledinto hard-shell gelatin capsules.

D. Suspension

    ______________________________________                                        Compound of formula (I)                                                                              100.0   mg                                             Dispersible Cellulose  100.0   mg                                             Glycerin               500.0   mg                                             Sucrose                3,500.0 mg                                             Flavouring Agent   q.s.                                                       Colouring Agent    q.s.                                                       Preserving Agent   0.1%                                                       Purified Water q.s. to 5.0     ml                                             ______________________________________                                    

The compound of formula (I) is suspended in the glycerin and a portionof the purified water. The sucrose and preserving agent are dissolved inanother portion of hot purified water, and then the colouring agent isadded and dissolved, followed by the dispersible cellulose. The twopreparations are mixed and cooled before the flavouring agent is added.Purified water is added to final volume. The resulting suspension isthroughly mixed.

E. IV Injection

    ______________________________________                                        Compound of formula (I)                                                                             5.0 mg                                                  Hydrochloric Acid     as needed for                                                                 pH adjustment                                           Water for Injections q.s. to                                                                         10 ml                                                  ______________________________________                                    

The compound of formula (I) is added to a portion of the Water forInjections. The pH is adjusted with hydrochloric acid to dissolve thecompound. Water for Injections is added to final volume and solution iscomplete after thorough mixing. The solution is sterilised by filtrationthrough a 0.22 micrometer membrane filter and aseptically filled intosterile 10 ml ampoules or vials.

I claim:
 1. A method of treating a lymphocytic leukemia in a host whichcomprises administering to said host an effective cytoxic amount of thecompound methylN-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamateor a pharmaceutically acceptable salt thereof.